Christoph Willibald Ritter von Gluck (2 July 1714 in Erasbach near Berching (Upper Palatinate) – 15 November 1787 in Vienna) was an opera composer of the early classical period. After many years at the Habsburg court at Vienna, Gluck brought about the practical reform of opera's dramaturgical practices that many intellectuals had been campaigning for over the years. With a series of radical new works in the 1760s, among them Orfeo ed Euridice and Alceste, he broke the stranglehold that Metastasian opera seria had enjoyed for much of the century.

The strong influence of French opera in these works encouraged Gluck to move to Paris, which he did in November 1773. Fusing the traditions of Italian opera and the French national genre into a new synthesis, Gluck wrote eight operas for the Parisian stages. One of the last of these, Iphigénie en Tauride, was a great success and is generally acknowledged to be his finest work. Though he was extremely popular and widely credited with bringing about a revolution in French opera, Gluck's mastery of the Parisian operatic scene was never absolute, and after the poor reception of his Echo et Narcisse, he left Paris in disgust and returned to Vienna to live out the remainder of his life.

Gluck was born in Erasbach (now a district of Berching, Bavaria) the first of six surviving children. His father, Alexander Johannes, came from a long line of foresters, and married Gluck's mother, Maria Walburga, in about 1711. During 1717 the family moved to Bohemia, where the father became head forester in the service of Prince Philipp Hyazinth von Lobkowitz in 1727. According to J.C. von Mannlich, who shared rooms with Gluck in Paris, it was as a Bohemian schoolboy that Gluck received his first musical training, both as a singer in the church choir and by learning. Gluck later wrote:

My father was a head forester in [Eisenberg] in Bohemia and he had brought me up to follow in his footsteps. At that time music was all the rage. Unfortunately, inflamed with a passion for this art, I soon made astounding progress and was able to play several instruments. My whole being became obsessed with music and I left all thoughts of a forester's life behind."

A childhood flight from home to Vienna is included in several contemporary accounts of Gluck's life, including Mannlich's, but recent scholarship has cast doubt on Gluck's picturesque tales of earning food and shelter by his singing as he travelled. Most now claim that, if this incident happened at all, it occurred later, and the object of Gluck's journeying was not Vienna but Prague, and connected to his studies at the University of Prague, where according to early biographies he began studying logic and mathematics in 1731. At this time the University boasted a flourishing musical scene that included performances of both Italian opera and oratorio. Gluck eventually left Prague without taking a degree, and vanishes from the historical record until 1737, a possible year (likely to have been 1736) in Vienna apart.

In 1737 Gluck arrived in Milan, where he studied under G.B. Sammartini, who, according to Carpani, taught Gluck "practical knowledge of all the instruments". Apparently this relationship lasted for several years. Sammartini was not, primarily, a composer of opera, his main output being of sacred music and symphonies, but Milan boasted a vibrant opera scene, and Gluck soon formed an association with one of the city's up-and-coming opera houses, the Teatro Regio Ducal, where his first opera, Artaserse, was performed on 26 December 1741. Set to a libretto by Metastasio, the opera opened the Milanese Carnival of 1742. According to one anecdote, the public would not accept Gluck's style until he inserted an aria in the lighter Milanese manner for contrast. Nevertheless, Gluck composed an opera for each of the next four Carnivals at Milan, with renowned castrato Giovanni Carestini appearing in many of the performances, so the reaction to Artaserse is unlikely to have been completely unfavourable. He also wrote operas for other cities of Northern Italy in between Carnival seasons, including Turin and Venice, where his Ipermestra was given during November 1744 at the Teatro San Giovanni Grisostomo. Nearly all of his operas in this period were, like Artaserse, set to Metastasio's texts, despite the poet's dislike for his style of composition.

In 1745 Gluck accepted an invitation to become house composer at London's King's Theatre, probably travelling to England via Frankfurt. The timing was poor, as the Jacobite Rebellion had caused much panic in London, and for most of the year the King's Theatre was shut. Gluck's two London operas, (La caduta de'giganti and Artamene) eventually performed in 1746, contained much borrowing from his earlier works, a method that was to re-occur throughout his career. Six trio sonatas were the other immediate fruits of his time in London. A more long-term benefit was exposure to the music of Handel, whom he later accounted a great influence on his style, and the naturalistic acting style of David Garrick. Handel's own experience of Gluck pleased that composer less — Charles Burney reports Handel as saying that "he [Gluck] knows no more of contrapunto, as mein cook, Waltz".

The years 1747 and 1748 brought Gluck two highly prestigious engagements. First came a commission to produce an opera for Dresden, performed by Pietro Mingotti's troupe, to celebrate a royal double wedding that would unite the ruling families of Bavaria and Saxony. Le nozze d'Ercole e d'Ebe, a festa teatrale, borrowed heavily from earlier works, and even from Gluck's teacher Sammartini. The success of this work brought Gluck to the attention of the Viennese court, and, ahead of such a figure as Johann Adolph Hasse, he was selected to set Metastasio's Semiramide riconosciuta to celebrate Maria Theresa's birthday. Vittoria Tesi took the title role. On this occasion Gluck's music was completely original, but the displeasure of Metastasio, the court poet, who called the opera "archvandalian music", probably explains why Gluck did not remain long in Vienna despite the work's enormous popular success (it was performed 27 times to great acclaim). For the remainder of 1748 and 1749 Gluck travelled with Mingotti's troupe, contracting a venereal disease from the prima donna and composing the opera La contesa de' numi for the court at Copenhagen.

In 1750 he abandoned Mingotti's group for another company established by a former member of the Mingotti troupe, Giovanni Battista Locatelli. The main effect of this was that Gluck returned to Prague on a more consistent basis. For the Prague Carnival of 1750 Gluck composed a new opera, Ezio (again set to one of Metastasio's works), and his Ipermestra was also performed in the same year. The other major event of Gluck's stay in Prague, on 15 September 1750, was his marriage to Maria Anna Bergin, aged 18 years old, the daughter of a long-dead rich Viennese merchant. The marriage brought Gluck financial security, and he seems to have spent most of 1751 commuting between Prague and Vienna.

The year 1752 brought another major commission to Gluck, when he asked to set Metastasio's La clemenza di Tito (the specific libretto was the composer's choice) for the nameday celebrations of King Charles III of Spain, held at Naples. The opera was performed on 4 November at the Teatro di San Carlo, and the world-famous mezzo-soprano castrato Caffarelli (Gaetano Majorano) took the role of Sextus. For Caffarelli Gluck composed the famous, but notoriously dissident, aria "Se mai senti spirarti sul volto", that provoked widespread admiration and equally widespread vituperation in equal measure. Gluck later reworked this aria for his Iphigénie en Tauride, which, according to one account, the Neapolitan composer Francesco Durante claimed that his fellow composers "should have been proud to have conceived and written". Durante simultaneously declined to comment concerning whether the aria was within the boundaries of the accepted compositional rules of the time.

Gluck finally settled in Vienna where he became Kapellmeister. He wrote Le Cinesi for a festival in 1754 and La Danza for the birthday of the future Emperor Leopold II the following year. After his opera Antigono was performed in Rome in February, 1756, Gluck was made a Knight of the Golden Spur by Pope Benedict XIV. From that time on, Gluck used the title "Ritter von Gluck" or "Chevalier de Gluck".

Gluck turned his back on Italian opera seria and began to write opéra comiques. In 1761, Gluck produced the groundbreaking ballet Don Juan in collaboration with the choreographer Gasparo Angiolini. The climax of Gluck's opéra comique writing was La rencontre imprévue of 1764. By that time, Gluck was already engaged in his operatic reforms.

Gluck had long pondered the fundamental problem of form and content in opera. He thought both of the main Italian operatic genres — opera buffa and opera seria — had strayed too far from what opera should really be. They seemed unnatural, the singing in opera seria was devoted to superficial effects, the content was uninteresting and fossilised. Opera buffa had long lost its original freshness, its jokes were threadbare, the repetition of the same characters made them seem no more than stereotypes. In opera seria too, the singers were effectively absolute masters of the stage and the music, decorating the vocal lines so floridly that audiences could no longer recognise the original melody. Gluck wanted to return opera to its origins, focusing on human drama and passions, and making words and music of equal importance. In Vienna, Gluck met likeminded figures in the operatic world: Count Giacomo Durazzo, the head of the court theatre, who was a passionate admirer of French stage music; the librettist Ranieri de' Calzabigi, who wanted to attack the dominance of Metastasian opera seria; the innovative choreographer Gasparo Angiolini; and the London-trained castrato Gaetano Guadagni.

The first result of the new thinking was Gluck's reformist ballet Don Juan, but a more important work was soon to follow. On 5 October 1762, Orfeo ed Euridice was given its first performance, with music by Gluck to words by Calzabigi. The dances were arranged by Angiolini and the title role was taken by Guadagni. Orfeo showed the beginnings of Gluck's reforms and the opera has never left the standard repertory. Gluck's idea was to make the drama of the work more important than the star singers who performed it, and to do away with dry recitative (recitativo secco, accompanied only by continuo) which broke up the action. The more flowing and dramatic style which resulted has been seen as a precursor to the music dramas of Richard Wagner. Gluck and Calzabigi followed Orfeo with Alceste (1767) and Paride ed Elena (1770), pushing their innovations even further. Calzabigi wrote a preface to Alceste, which Gluck signed, setting out the principles of their reforms.

Gluck now began to spread his ideas to France. Under the patronage of his former music pupil, Marie Antoinette, who had married the future French king Louis XVI in 1770, Gluck signed a contract for six stage works with the management of the Paris Opéra. He began with Iphigénie en Aulide (19 April 1774). The premiere sparked a huge controversy, almost a war, such as had not been seen in the city since the Querelle des Bouffons. Gluck's opponents brought the leading Italian composer, Niccolò Piccinni, to Paris to demonstrate the superiority of Neapolitan opera and the "whole town" engaged in an argument between "Gluckists" and "Piccinnists". The composers themselves took no part in the polemics, but when Piccinni was asked to set the libretto to Roland, on which Gluck was also known to be working, Gluck destroyed everything he had written for that opera up to that point.

On 2 August 1774 the French version of Orfeo ed Euridice was performed, with the title role transposed from the castrato to the tenor voice. This time Gluck's work was better received by the Parisian public. In the same year Gluck returned to Vienna where he was appointed composer to the imperial court. Over the next few years the now internationally famous composer would travel back and forth between Paris and Vienna. On 23 April 1776, the French version of Alceste was given.

Gluck also wrote Armide (1777), Iphigénie en Tauride (1779) and Echo et Narcisse for Paris. During the rehearsals for Echo et Narcisse, Gluck suffered his first stroke. Since the opera itself was a complete failure, Gluck decided to return to Vienna.

His musical heir in Paris was the composer Antonio Salieri, who had been Gluck's protégé since he arrived in Vienna in 1767, and later had made friends with Gluck. Gluck brought Salieri to Paris with him and bequeathed him the libretto for Les Danaïdes by Leblanc du Roullet and Baron Tschudi. The opera was announced as a collaboration between the two composers; however, after the overwhelming success of its premiere on 26 April 1784, Gluck revealed to the prestigious Journal de Paris that the work was wholly Salieri's.

In Vienna Gluck wrote a few more minor works but he generally lived in retirement. In 1781 he brought out a German version of Iphigénie en Tauride and other operas of his enjoyed great popularity in Vienna.

On 15 November 1787, in Vienna, Gluck suffered another stroke and died a few days later. At a formal commemoration on 8 April 1788 his friend and pupil Salieri conducted Gluck's De profundis and a requiem by the Italian composer Niccolò Jommelli was given. Like many other prominent musicians and painters, Gluck was buried in the Matzleinsdorfer Friedhof. When this cemetery was turned into a park in 1923, Gluck's remains were transferred to a tomb in the Vienna Zentralfriedhof.

Gluck's musical legacy was around 35 complete operas, together with numerous ballets and instrumental works. His reforms influenced Mozart, particularly his opera Idomeneo (1781). Gluck left behind a flourishing school of disciples in Paris, who would dominate the French stage throughout the Revolutionary and Napoleonic period. As well as Salieri, they included Sacchini, Cherubini, Méhul and Spontini. Gluck's greatest French admirer would be Hector Berlioz, whose epic Les Troyens may be seen as the culmination of the Gluckian tradition. Though Gluck wrote no operas in German, his example influenced the German school of opera, particularly Weber and Wagner, whose concept of music drama was not so far removed from Gluck's own.