John Dee (13 July 1527 – 1608 or 1609) was a noted mathematician, astronomer, astrologer, occultist, navigator, imperialist, and consultant to Queen Elizabeth I. He devoted much of his life to the study of alchemy, divination, and Hermetic philosophy.

Dee straddled the worlds of science and magic just as they were becoming distinguishable. One of the most learned men of his age, he had been invited to lecture on advanced algebra at the University of Paris while still in his early twenties. Dee was an ardent promoter of mathematics and a respected astronomer, as well as a leading expert in navigation, having trained many of those who would conduct England's voyages of discovery. In one of several tracts which Dee wrote in the 1580s encouraging British exploratory expeditions in search of the Northwest Passage, he appears to have coined (or at least introduced into print) the term "British Empire." Simultaneously with these efforts, Dee immersed himself in the worlds of magic, astrology, and Hermetic philosophy. He devoted much time and effort in the last thirty years or so of his life to attempting to commune with angels in order to learn the universal language of creation and bring about the pre-apocalyptic unity of mankind. A student of the Renaissance Neo-Platonism of Marsilio Ficino, Dee did not draw distinctions between his mathematical research and his investigations into Hermetic magic, angel summoning and divination. Instead he considered all of his activities to constitute different facets of the same quest: the search for a transcendent understanding of the divine forms which underlie the visible world, which Dee called "pure verities". Dee's high status as a scholar also allowed him to play a role in Elizabethan politics. He served as an occasional adviser and tutor to Elizabeth I and nurtured relationships with her ministers Francis Walsingham and William Cecil. Dee also tutored and enjoyed patronage relationships with Sir Philip Sidney, his uncle Robert Dudley, 1st Earl of Leicester, and Edward Dyer. He also enjoyed patronage from Sir Christopher Hatton. In his lifetime Dee amassed the largest library in England and one of the largest in Europe.

Dee was born in Tower Ward, London, to a Welsh family, whose surname derived from the Welsh du ("black"). His father Roland was a mercer and minor courtier. Dee's family arrived in London in the wake of the Welshman Henry Tudor's coronation as Henry VII.

Dee attended the Chelmsford Catholic School from 1535 (now King Edward VI Grammar School (Chelmsford)), then – from November 1542 to 1546 – St. John's College, Cambridge. His great abilities were recognized, and he was made a founding fellow of Trinity College, where the clever stage effects he produced for a production of Aristophanes' Peace procured him the reputation of being a magician that clung to him through life. In the late 1540s and early 1550s, he travelled in Europe, studying at Leuven (1548) and Brussels and lecturing in Paris on Euclid. He studied with Gemma Frisius and became a close friend of the cartographer Gerardus Mercator, returning to England with an important collection of mathematical and astronomical instruments. In 1552, he met Gerolamo Cardano in London: during their acquaintance they investigated a perpetual motion machine as well as a gem purported to have magical properties.

Rector at Upton-upon-Severn from 1553, Dee was offered a readership in mathematics at Oxford in 1554, which he declined; he was occupied with writing and perhaps hoping for a better position at court. In 1555, Dee became a member of the Worshipful Company of Mercers, as his father had, through the company's system of patrimony.

That same year, 1555, he was arrested and charged with "calculating" for having cast horoscopes of Queen Mary and Princess Elizabeth; the charges were expanded to treason against Mary. Dee appeared in the Star Chamber and exonerated himself, but was turned over to the Catholic Bishop Bonner for religious examination. His strong and lifelong penchant for secrecy perhaps worsening matters, this entire episode was only the most dramatic in a series of attacks and slanders that would dog Dee throughout his life. Clearing his name yet again, he soon became a close associate of Bonner.

Dee presented Queen Mary with a visionary plan for the preservation of old books, manuscripts and records and the founding of a national library, in 1556, but his proposal was not taken up. Instead, he expanded his personal library at his house in Mortlake, tirelessly acquiring books and manuscripts in England and on the European Continent. Dee's library, a center of learning outside the universities, became the greatest in England and attracted many scholars.

When Elizabeth took the throne in 1558, Dee became her trusted advisor on astrological and scientific matters, choosing Elizabeth's coronation date himself. From the 1550s through the 1570s, he served as an advisor to England's voyages of discovery, providing technical assistance in navigation and ideological backing in the creation of a "British Empire", a term that he was the first to use. Dee wrote a letter to William Cecil, 1st Baron Burghley, in October 1574 seeking patronage. He claimed to have occult knowledge of treasure on the Welsh Marches, and of ancient valuable manuscripts kept at Wigmore Castle, knowing that the Lord Treasurer's ancestors came from this area. In 1577, Dee published General and Rare Memorials pertayning to the Perfect Arte of Navigation, a work that set out his vision of a maritime empire and asserted English territorial claims on the New World. Dee was acquainted with Humphrey Gilbert and was close to Sir Philip Sidney and his circle.

In 1564, Dee wrote the Hermetic work Monas Hieroglyphica ("The Hieroglyphic Monad"), an exhaustive Cabalistic interpretation of a glyph of his own design, meant to express the mystical unity of all creation. He travelled to Hungary to present a copy personally to Maximilian II, Holy Roman Emperor. This work was highly valued by many of Dee's contemporaries, but the loss of the secret oral tradition of Dee's milieu makes the work difficult to interpret today. In an edition of the popular TV series "QI" first screened on BBC1 on 2 April 2010, host Stephen Fry stated that the code '007' used to refer to James Bond was derived from this glyph.

He published a "Mathematical Preface" to Henry Billingsley's English translation of Euclid's Elements in 1570, arguing the central importance of mathematics and outlining mathematics' influence on the other arts and sciences. Intended for an audience outside the universities, it proved to be Dee's most widely influential and frequently reprinted work.

From 1570 Dee advocated a policy of political and economic strengthening of England and imperial expansion into the New World. In his manuscript, Brytannicae reipublicae synopsis (1570), he outlined the current state of the Elizabethan Realm and was concerned with trade, ethics, and national strength.

His 1576 General and rare memorials pertayning to the Perfect Arte of Navigation, was the first volume in an unfinished series planned to advocate the rise of imperial expansion. In the highly symbolic frontispiece, Dee included a figure of Britannia kneeling by the shore beseeching Elizabeth I, to protect her empire by strengthening her navy. Dee used Geoffrey's inclusion of Ireland in Arthur's imperial conquests to argue that Arthur had established a ‘British empire’ abroad. He further argued that England exploit new lands through colonization and this vision could become reality through maritime supremacy. In making these arguments, Dee is credited with the earliest use in English of the terms Brytish Iles and Brytish Impire.

Dee posited a formal claim to North America on the back of a map drawn in 1577–80; he noted Circa 1494 Mr Robert Thorn his father, and Mr Eliot of Bristow, discovered Newfound Land.  In his Title Royal of 1580, he invented the claim that Madog ab Owain Gwynedd had discovered America with Dee intending to prove that England's claim to the New World was stronger than that of Spain. He further asserted that Brutus of Britain and King Arthur as well as Madog had conquered lands in the Americas and therefore their heir Elizabeth I of England had a priority claim there.

By the early 1580s, Dee was growing dissatisfied with his progress in learning the secrets of nature and with his own lack of influence and recognition. He began to turn towards the supernatural as a means to acquire knowledge. Specifically, he sought to contact angels through the use of a "scryer" or crystal-gazer, who would act as an intermediary between Dee and the angels. Dee's first attempts were not satisfactory, but, in 1582, he met Edward Kelley (then going under the name of Edward Talbot), who impressed him greatly with his abilities. Dee took Kelley into his service and began to devote all his energies to his supernatural pursuits. These "spiritual conferences" or "actions" were conducted with an air of intense Christian piety, always after periods of purification, prayer and fasting. Dee was convinced of the benefits they could bring to mankind. (The character of Kelley is harder to assess: some have concluded that he acted with complete cynicism, but delusion or self-deception are not out of the question. Kelley's "output" is remarkable for its sheer mass, its intricacy and its vividness.) Dee maintained that the angels laboriously dictated several books to him this way, some in a special angelic or Enochian language.

In 1583, Dee met the visiting Polish nobleman Albert Łaski, who invited Dee to accompany him on his return to Poland. With some prompting by the angels, Dee was persuaded to go. Dee, Kelley, and their families left for the Continent in September 1583, but Łaski proved to be bankrupt and out of favour in his own country. Dee and Kelley began a nomadic life in Central Europe, but they continued their spiritual conferences, which Dee recorded meticulously. He had audiences with Emperor Rudolf II and King Stephen of Poland and attempted to convince them of the importance of his angelic communications. Particularly interesting was his meeting with the Polish King Stephan. The event happened at the royal castle at Niepołomice (near Kraków, then the capital of Poland) and was later widely analysed by Polish historians (Ryszard Zieliński, Roman Żelewski, Roman Bugaj) and writers (Waldemar Łysiak). While generally they accepted him as being a man of wide and deep knowledge they also pointed out his connections with the English monarch Elizabeth. This prompted them to conclude that the meeting could have hidden political goals. Nevertheless, the Polish King who, being a devout Catholic, was very cautious of any supernatural media, started the meeting with a statement that all prophetic revelations were finalised with the mission of Jesus Christ. He also stressed that he would take part in the event provided that there would be nothing against the teaching of the Holy Catholic Church.

During a spiritual conference in Bohemia, in 1587, Kelley told Dee that the angel Uriel had ordered that the two men should share their wives. Kelley, who by that time was becoming a prominent alchemist and was much more sought-after than Dee, may have wished to use this as a way to end the spiritual conferences. The order caused Dee great anguish, but he did not doubt its genuineness and apparently allowed it to go forward, but broke off the conferences immediately afterwards and did not see Kelley again. Dee returned to England in 1589.

Dee returned to Mortlake after six years to find his library ruined and many of his prized books and instruments stolen. He sought support from Elizabeth, who finally made him Warden of Christ's College, Manchester, in 1595. This former College of Priests had been re-established as a Protestant institution by a Royal Charter of 1578. However, he could not exert much control over the Fellows, who despised or cheated him. Early in his tenure, he was consulted on the demonic possession of seven children, but took little interest in the matter, although he did allow those involved to consult his still extensive library.

He left Manchester in 1605 to return to London, however he remained Warden until his death. By that time, Elizabeth was dead, and James I, unsympathetic to anything related to the supernatural, provided no help. Dee spent his final years in poverty at Mortlake, forced to sell off various of his possessions to support himself and his daughter, Katherine, who cared for him until the end. He died in Mortlake late in 1608 or early 1609 aged 82 (there are no extant records of the exact date as both the parish registers and Dee's gravestone are missing).

Dee was married twice and had eight children. Details of his first marriage are sketchy, but is likely to have been from 1565 to his wife's death in around 1576. From 1577 to 1601 Dee kept a meticulous diary. In 1578 he married the twenty-three year old Jane Fromond (Dee was fifty-one at the time). She was to be the wife that Kelley claimed Uriel had demanded that he and Dee share, and although Dee complied for a while this eventually caused the two men to part company. Jane died during the plague in Manchester and was buried in March 1604, along with a number of his children: Theodore is known to have died in Manchester, but although no records exist for his daughters Madinia, Frances and Margaret after this time, Dee had by this time ceased keeping his diary. His eldest son was Arthur Dee, about whom Dee wrote a letter to his headmaster at Westminster School which echoes the worries of boarding school parents in every century; Arthur was also an alchemist and hermetic author. The antiquary John Aubrey gives the following description of Dee: "He was tall and slender. He wore a gown like an artist's gown, with hanging sleeves, and a slit.... A very fair, clear sanguine complexion... a long beard as white as milk. A very handsome man."

Dee was an intensely pious Christian, but his Christianity was deeply influenced by the Hermetic and Platonic - Pythagorean doctrines that were pervasive in the Renaissance. He believed that numbers were the basis of all things and the key to knowledge, that God's creation was an act of numbering. From Hermeticism, he drew the belief that man had the potential for divine power, and he believed this divine power could be exercised through mathematics. His cabalistic angel magic (which was heavily numerological) and his work on practical mathematics (navigation, for example) were simply the exalted and mundane ends of the same spectrum, not the antithetical activities many would see them as today. His ultimate goal was to help bring forth a unified world religion through the healing of the breach of the Catholic and Protestant churches and the recapture of the pure theology of the ancients.

About ten years after Dee's death, the antiquarian Robert Cotton purchased land around Dee's house and began digging in search of papers and artifacts. He discovered several manuscripts, mainly records of Dee's angelic communications. Cotton's son gave these manuscripts to the scholar Méric Casaubon, who published them in 1659, together with a long introduction critical of their author, as A True & Faithful Relation of What passed for many Yeers between Dr. John Dee (A Mathematician of Great Fame in Q. Eliz. and King James their Reignes) and some spirits. As the first public revelation of Dee's spiritual conferences, the book was extremely popular and sold quickly. Casaubon, who believed in the reality of spirits, argued in his introduction that Dee was acting as the unwitting tool of evil spirits when he believed he was communicating with angels. This book is largely responsible for the image, prevalent for the following two and a half centuries, of Dee as a dupe and deluded fanatic.

Around the same time the True and Faithful Relation was published, members of the Rosicrucian movement claimed Dee as one of their number. There is doubt, however, that an organized Rosicrucian movement existed during Dee's lifetime, and no evidence that he ever belonged to any secret fraternity. Dee's reputation as a magician and the vivid story of his association with Edward Kelley have made him a seemingly irresistible figure to fabulists, writers of horror stories and latter-day magicians. The accretion of false and often fanciful information about Dee often obscures the facts of his life, remarkable as they are in themselves.

A re-evaluation of Dee's character and significance came in the 20th century, largely as a result of the work of the historian Frances Yates, who brought a new focus on the role of magic in the Renaissance and the development of modern science. As a result of this re-evaluation, Dee is now viewed as a serious scholar and appreciated as one of the most learned men of his day. His personal library at Mortlake was the largest in the country, and was considered one of the finest in Europe, perhaps second only to that of de Thou. As well as being an astrological and scientific advisor to Elizabeth and her court, he was an early advocate of the colonization of North America and a visionary of a British Empire stretching across the North Atlantic. The term "British Empire" is in fact Dee's own invention. Dee promoted the sciences of navigation and cartography. He studied closely with Gerardus Mercator, and he owned an important collection of maps, globes and astronomical instruments. He developed new instruments as well as special navigational techniques for use in polar regions. Dee served as an advisor to the English voyages of discovery, and personally selected pilots and trained them in navigation. He believed that mathematics (which he understood mystically) was central to the progress of human learning. The centrality of mathematics to Dee's vision makes him to that extent more modern than Francis Bacon, though some scholars believe Bacon purposely downplayed mathematics in the anti-occult atmosphere of the reign of James I. It should be noted, though, that Dee's understanding of the role of mathematics is radically different from our contemporary view. Dee's promotion of mathematics outside the universities was an enduring practical achievement. His "Mathematical Preface" to Euclid was meant to promote the study and application of mathematics by those without a university education, and was very popular and influential among the "mecanicians": the new and growing class of technical craftsmen and artisans. Dee's preface included demonstrations of mathematical principles that readers could perform themselves.

Dee was a friend of Tycho Brahe and was familiar with the work of Copernicus. Many of his astronomical calculations were based on Copernican assumptions, but he never openly espoused the heliocentric theory. Dee applied Copernican theory to the problem of calendar reform. His sound recommendations were not accepted, however, for political reasons.

He has often been associated with the Voynich Manuscript. Wilfrid M. Voynich, who bought the manuscript in 1912, suggested that Dee may have owned the manuscript and sold it to Rudolph II. Dee's contacts with Rudolph were far less extensive than had previously been thought, however, and Dee's diaries show no evidence of the sale. Dee was, however, known to have possessed a copy of the Book of Soyga, another enciphered book.

At Elizabeth I's request Dee embraced the old Welsh 'Prince Madog' myth to lay claim to North America. The well known story was of a young Welsh prince who discovered America in 1170, over three hundred years before Christopher Columbus's voyage in 1492. The fact was that Elizabeth I had little interest in the New World and Dee's hopes were premature.

The British Museum holds several items once owned by Dee and associated with the spiritual conferences.