Christoph Willibald (Ritter von) Gluck (/ɡlʊk/; German: [ˈkʁɪstɔf ˈvɪlɪbalt ˈɡlʊk]; 2 July 1714 – 15 November 1787) was a composer of Italian and French opera in the early classical period. Born in the Upper Palatinate and raised in Bohemia, both part of the Holy Roman Empire at the time, he gained prominence at the Habsburg court in Vienna. There he brought about the practical reform of opera's dramaturgical practices for which many intellectuals had been campaigning. 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. Gluck introduced more drama by using orchestral recitative and cutting the usually long da capo aria. His later operas have half the length of a typical baroque opera.

The strong influence of French opera encouraged Gluck to move to Paris in November 1773. Fusing the traditions of Italian opera and the French (with rich chorus) into a unique synthesis, Gluck wrote eight operas for the Parisian stage. Iphigénie en Tauride (1779) was a great success and is often considered 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. After the poor reception of his Echo et Narcisse (1779), he left Paris in disgust and returned to Vienna to live out the remainder of his life.

Gluck's earliest known ancestor is his great-grandfather, Simon Gluckh von Rockenzahn, whose name is recorded in the marriage contract (1672) of his son, the forester Johann (Hans) Adam Gluck (c. 1649–1722) and grandfather of Christoph. 'Rockenzahn' is believed to be Rokycany, located in the central part of western Bohemia (about 70 km southwest of Prague and 16 km east of Pilsen). The family name Gluck (also spelled Gluckh, Klugh, Kluch, etc.) likely comes from the Czech word for boy (kluk). In its various spellings, it is repeatedly found in the records of Rokycany. Around 1675 Hans Adam moved to Neustadt an der Waldnaab in the service of Prince Ferdinand August von Lobkowitz, who possessed extensive landholdings in Bohemia as well as the county of Störnstein-Neustadt in the Upper Palatinate.

Gluck's father, Alexander, was born in Neustadt an der Waldnaab on 28 October 1683, one of four sons of Hans Adam Gluck who became foresters or gamekeepers. Alexander served in a contingent of about 50 soldiers under Philipp Hyazinth von Lobkowitz, the son of Ferdinand August von Lobkowitz, during the War of Spanish Succession, and, according to Gluck family tradition, rose to the level of gunbearer to the great general of the imperial forces, Eugene of Savoy. In 1711 Alexander settled outside Berching as a forester and hunter in the service of the monastery Seligenporten, Plankstetten Abbey, and the mayors of Neumarkt in der Oberpfalz. He took the vacant position of hunter in Erasbach in 1711 or 1712 (his predecessor had been found shot in the forest).

About Gluck's mother, Maria Walburga, almost nothing is known, including her surname, but she probably grew up in the same area as she was named after Saint Walburga, the sister of Saint Willibald, the first bishop of nearby Eichstätt. The couple probably married around 1711. In 1713 Alexander built a house in Erasbach and by 12 September had taken possession of it.

Although there is no documentary record with Gluck's birthdate at the time of his birth, he himself gave it as 2 July 1714 on an official document requested by Paris that he signed in 1785 in Vienna in the presence of the French ambassador Emmanuel Marie Louis de Noailles. This has long been the commonly accepted date. He was baptized Christophorus Willibaldus on 4 July 1714 in the village of Weidenwang, a parish that at that time also included Erasbach. Gluck himself never used the name Willibald. The church in Weidenwang was consecrated to Saint Willibald (as was the entire Eichstätt diocese to which it belonged), and the name Willibald is frequently found in the baptismal register, often as a second name. No documents contemporary with Gluck's life use the name Willibald. Only in the 19th century did scholars begin using it to distinguish the composer from his father's brother Johann Christoph, born in 1700, whose baptism had earlier been confused with that of the composer.

In the year of Gluck's birth, the Treaty of Rastatt and the Treaty of Baden ended the War of Spanish Succession and brought Erasbach under Bavarian control. Gluck's father had to reapply to retain his position and received no salary until after 1715, when he began receiving 20 gulden. He obtained additional employment in the vicinity of Weidenwang in 1715 as a forester in the service of Seligenporten Monastery, and after 1715, also with Plankstetten Abbey. In 1716 Alexander Gluck was cited for poor performance and warned he might be terminated. He sold his house in August 1717 and voluntarily left Erasbach near the end of September to take up employment as head forester in Reichstadt, serving the Duchess of Tuscany, the wealthy Anna Maria Franziska of Saxe-Lauenburg, since 1708 separated from her husband Gian Gastone de' Medici, the last duke of Tuscany.

On 1 April 1722 Alexander Gluck took a position as forest-master under Count Philipp Joseph von Kinsky in Böhmisch Kamnitz, where Kinsky had increased his domains. The family moved to the forester's house in nearby Oberkreibitz.