Albrecht Wenzel Eusebius von Wallenstein (24 September 1583 – 25 February 1634), also known as Albrecht von Waldstein, was a Bohemian soldier and politician, who offered his services, and an army of 30,000 to 100,000 men during the Danish period (1625 – 1629) of the Thirty Years' War (1618 – 1648), to the Holy Roman Emperor Ferdinand II. He became the supreme commander of the armies of the Habsburg Monarchy and one of the major figures of the Thirty Years' War.

A successful generalissimo who had made himself ruler of the lands of the Duchy of Friedland in northern Bohemia, Wallenstein found himself released from service in 1630 after Ferdinand grew wary of his ambition. Several Protestant victories over Catholic armies induced Ferdinand to recall Wallenstein, who again turned the war in favor of the Imperial cause. Dissatisfied with the emperor's treatment of him, Wallenstein considered allying with the Protestants. However, Ferdinand had the general assassinated at Eger (Cheb) in Egerland by one of the army's officials, Walter Devereux.

Wallenstein, born in Heřmanice, Bohemia, into a poor Protestant branch of an old noble family, lost both his parents, Vilém of Waldstein and Markéta of Smiřický at the age of 12. His maternal uncle, Albrecht Slavata of Chlum and Košumberk, raised him and sent him to the school of the Unity of the Brethren at Košumberk Castle (Eastern Bohemia) and to the Protestant grammar school at Goldberg in Silesia. From 1599 Wallenstein continued his education at the University of Altdorf and then at the universities of Bologna and Padua.

Wallenstein then joined the army of Rudolf II in Hungary, where he saw, under the command of Giorgio Basta, two years of armed service (1604 – 1606) against the Ottoman Turks and Hungarian rebels. In 1606 he converted to Catholicism due to his friendship with Jesuits and with the Habsburgs. He studied at University of Olomouc (matriculated 1605). Wallenstein later would owe allegiance to the Imperial Habsburg Monarchy as a member of the Order of the Golden Fleece. Even though he was religious, Wallenstein did not become a zealot. Three years later he returned to Bohemia and soon married Lucretia of Landek, a rich widow three years older than himself, whose estates in Moravia he inherited after her death in 1614. He used his wealth to win favour, offering and commanding 200 horses for Archduke Ferdinand of Styria for his war with Venice in 1617, thereby relieving the fortress of Gradisca from Venetian siege. He later endowed a monastery in her name, and had her reburied there. In 1617 Wallenstein married Isabella Katharina, daughter of Count Harrach. She bore him two children, a son who died in infancy and a surviving daughter. Examples of the couple's correspondence survive. Both marriages made him one of the wealthiest men in the Bohemian Crown.

The Thirty Years' War began in 1618 when the estates of Bohemia rebelled against Ferdinand of Styria and elected Frederick V, Elector Palatine, the leader of the Protestant Union, as their new king. Wallenstein associated himself with the cause of the Catholics and the Habsburg dynasty. Sympathizing with the Bohemians, he used his position as commander of the troops of the Moravian estates to escape with the Moravian treasure chest to Vienna. There, however, the authorities told him that the money would go back to the province — but he had shown his loyalty to Ferdinand, the future Emperor.

Wallenstein equipped a regiment of cuirassiers and won great distinction under Charles Bonaventure de Longueval, Count of Bucquoy in the wars against Ernst von Mansfeld and Gabriel Bethlen (both supporters of the Bohemian revolt) in Moravia. Wallenstein recovered his lands (which the rebels had seized in 1619) and after the Battle of White Mountain (8 November 1620) he secured the estates belonging to his mother's family and confiscated tracts of Protestant lands. He grouped his new possessions into a territory called Friedland (Frýdlant) in northern Bohemia. A series of successes in battle led to Wallenstein becoming in 1622 an imperial count palatine, in 1623 a prince, and in 1625 Duke of Friedland. Wallenstein proved an able administrator of the duchy and also sent a large representation to Prague to emphasize his nobility.

In order to aid Ferdinand (elected Holy Roman Emperor in 1619) against the Northern Protestants and to produce a balance in the Army of the Catholic League under Johann Tserclaes, Count of Tilly, Wallenstein offered to raise a whole army for the imperial service following the bellum se ipsum alet principle, and received his final commission on 25 July 1625. Wallenstein’s success as a military commander brought him fiscal credit, which in turn enabled him to receive loans to buy lands, many of them being the former estates of conquered Bohemian nobles. Wallenstein also used his credit to grant loans to Ferdinand II, who then repaid him through lands and titles. Wallenstein's popularity soon recruited 30,000 (not long afterwards 50,000) men. The two armies worked together over 1625 – 1627, at first against Mansfeld.

Having beaten Mansfeld at Dessau (25 April 1626), Wallenstein cleared Silesia of the remnants of Mansfeld's army in 1627. At this time he bought from the emperor the Duchy of Sagan (in Silesia). He then joined Tilly in the struggle with Christian IV of Denmark, and afterwards gained as a reward the Duchies of Mecklenburg, whose hereditary dukes suffered expulsion for having helped the Danish king. This awarding of a major territory to someone of the lower nobility shocked the high-born rulers of many other German states.

Wallenstein assumed the title of "Admiral of the North and Baltic Seas". However, in 1628 he failed to capture Stralsund, which resisted the Capitulation of Franzburg and the subsequent siege with assistance of Danish, Scottish and Swedish troops, a blow that denied him access to the Baltic and the chance of challenging the naval power of the Scandinavian kingdoms and of the Netherlands. Though he succeeded in defeating Christian IV of Denmark in the Battle of Wolgast and neutralizing Denmark in the subsequent Peace of Lübeck, the situation further deteriorated when the presence of the Imperial catholic troops on the Baltic and the Emperor's "Edict of Restitution" brought King Gustavus Adolphus of Sweden into the conflict. He attempted to aid forces of the Polish - Lithuanian Commonwealth under Hetman Stanisław Koniecpolski, which were fighting Sweden in 1629; however, Wallenstein failed to engage any major Swedish forces and this significantly affected the outcome of the conflict.

Over the course of the war Wallenstein's ambitions and the exactions of his army had made him a host of enemies, both Catholic and Protestant princes and non-princes. Ferdinand suspected Wallenstein of planning a coup to take control of the Holy Roman Empire. The Emperor's advisors advocated dismissing him, and in September 1630 envoys were sent to Wallenstein to announce his removal. Wallenstein gave over his army to General Tilly, and retired to Jitschin (Jičín), the capital of his Duchy of Friedland. There he lived in an atmosphere of "mysterious magnificence".

However, circumstances forced Ferdinand to call Wallenstein into the field again. The successes of Gustavus Adolphus over General Tilly at the Battle of Breitenfeld and on the Lech (1632), where Tilly was killed, and his advance to Munich and occupation of Bohemia, demanded action. In the spring of 1632 Wallenstein raised a fresh army within a few weeks and took the field. He drove the Saxon army from Bohemia and then advanced against Gustavus Adolphus, whom he opposed near Nuremberg and after the Battle of the Alte Veste dislodged. In November came the great Battle of Lützen, in which Wallenstein was forced to retreat but in the confused melee, Gustavus Adolphus was killed. Wallenstein then withdrew to winter quarters in Bohemia.

In the campaigning of 1633 Wallenstein's apparent unwillingness to attack the enemy caused much concern in Vienna and in Spain. At this time the dimensions of the war grew more European. Wallenstein had, in fact, started preparing to desert the Emperor: he expressed anger at Ferdinand's refusal to revoke the Edict of Restitution. History records little about his secret negotiations; but rumors told that he was preparing to force a just peace on the Emperor in the interests of united Germany, at the same time hesitating — as he used to do in other respects — and trying to stay loyal to the Emperor as far as possible. With this apparent "plan" he entered into negotiations with Saxony, Brandenburg, Sweden, and France. But apparently the Habsburgs' enemies tried to draw him to their side. In any case, he gained little support. Anxious to make his power felt, he at last resumed the offensive against the Swedes and Saxons, winning his last victory at Steinau on the Oder in October. He then resumed negotiations.

In December Wallenstein retired with his army to Bohemia, around Pilsen. Vienna soon definitely convinced itself of his treachery, a secret court found him guilty, and the Emperor sought for serious means of getting rid of him (a successor - in - command, the later emperor Ferdinand III, was already waiting). Wallenstein was aware of the plan to replace him, but felt confident that when the army came to decide between him and the Emperor the decision would be in his favour.

On 24 January 1634 the Emperor signed a secret patent (opened only to certain of Wallenstein's officers) removing him from his command. Finally an open patent charging Wallenstein with high treason was signed on 18 February and published in Prague. Losing the support of his army, Wallenstein now realized the extent of his peril, and on 23 February with a company of some hundred men, he went from Pilsen to Eger (Cheb), hoping to meet the Swedes under Duke Bernhard. After having arrived at Eger, however, certain senior Scottish and Irish officers in his force assassinated him on the night of 25 February.

To carry out the assassination, a regiment of dragoons under the command of an Irish Colonel Butler and the Scots colonels Walter Leslie and John Gordon first rushed upon Wallenstein's trusted officers Terzky, Kinsky, Illo and Neumann whilst the latter banqueted at Cheb Castle (which had come under the command of John Gordon himself), and massacred them. Terzky alone managed to fight his way out into the courtyard, only to be shot down by a group of musketeers.

A few hours later, an Irish captain, Walter Devereux, together with a few companions, broke into the burgomaster's house at the main square, where Wallenstein had his lodgings (again courtesy of John Gordon), and kicked open the bedroom door, whereupon Devereux ran his halberd through the unarmed Wallenstein, who, roused from sleep, is said to have asked in vain for quarter.

The Holy Roman Emperor may not have commanded the murder, nor may he definitely desired it; but he had given free rein to the party who he knew wished "to bring in Wallenstein, alive or dead." After the assassination, he rewarded the murderers with honour and riches.

Wallenstein was buried at Jitschin (Jičín).

The Czech National Museum produced a large exhibition about Wallenstein at the Wallenstein Palace in Prague (current seat of Senate) from 15 November 2007 till 15 February 2008. He is also the subject of Schiller's play trilogy Wallenstein. One of the episodes in Erich Kästner's "The 35 May" depicts Wallenstein in his afterlife being engaged in a fierce war with Hannibal and emphasizes both generals' callous disregard for the lives of their soldiers - underlining Kästner's pacifist views.

Wallenstein's particular genius lay in recognizing a new way for funding war: instead of merely plundering enemies, he called for a new method of systematic "war taxes". Even a city or a prince on the side of the Emperor had to pay taxes towards the war. He understood the enormous wastage of resources that resulted from tax exactions on princes and cities of defeated enemies only, and desired to replace this with a "balanced" system of taxation; wherein both sides bore the cost of a war. He was unable to fully realize this ambition; and in fact his idea led to the random exploitation of whole populations on either side, until finally, almost fifteen years after his death, the war had become so expensive that the warring parties were forced to make peace. In any case, Wallenstein's idea inspired many, among them, Colbert, to "pluck the goose with a minimum of screeching".

Composer Bedřich Smetana honored Wallenstein in his 1859 symphonic poem Wallenstein's Camp, which was originally intended as an overture to a play by Schiller.