Don Juan Manuel (5 May 1282 – 13 June 1348) was a Spanish medieval writer, nephew of Alfonso X of Castile, son of Manuel of Castile and Beatrice of Savoy. He inherited from his father the great Lordship of Villena, receiving the titles of Lord, Duke and lastly Prince of Villena. He married three times, choosing his wives for political and economic convenience, and worked to match his children with partners associated with royalty. Juan Manuel became one of the richest and most powerful men of his time, coining his own currency as the kings did. During his life, he was criticised for choosing literature as his vocation, an activity thought inferior for a nobleman of such prestige.

Some confusion exists about his names and titles. Juan Manuel often refers to himself in his books as "Don Juan, son of infante don Manuel". But some 19th and early 20th century scholars started calling him infante, a title he did not possess, as in medieval Castile only the sons of kings were called infantes (and he was the grandson of Fernando III). The same applies for the title of Duke and Prince of Villena, that he received from Alfonso IV and Pedro IV of Aragón. As these titles follow the Aragonese nobiliary traditions, they were of little interest to the Castilian author, to the point that he never used them in his writings or correspondence, and they have only been associated to him by a handful of scholars.

Juan Manuel was born in the Castle of Escalona, in what is now the province of Toledo. He was a son of Manuel of Castile (son of Ferdinand III of Castile) and his second wife Beatrice of Savoy. His father died in 1284, and Juan was educated at the court of his cousin, Sancho IV, with whom his abilities made him a favourite. With the death of his mother in 1292, Juan Manuel became duke of Peñafiel. Juan Manuel was trained in arts such as equestrianism, hunting, and fencing, and in addition learned Latin, history, law, and theology. At the age of twelve, he fought to repel the attack of the Moors from Granada to Murcia.

In 1304 he was entrusted by the queen mother, Doña María de Molina, to conduct political negotiations with James II of Aragon on behalf of her son, Ferdinand IV, then under age. The diplomacy was successful and Juan Manuel's marriage to James II's daughter, Constance, added to his prestige.

Juan Manuel gave the hand of his daughter Constanza in marriage to Alfonso XI, with whom he had constant confrontations. However, the king kept Constanza as a prisoner in the Castle of Toro for unclear reasons. This incident angered Juan Manuel, who decided to turn against Alfonso. He declared war on the monarch, beginning a long confrontation.

On the death of his wife Constance in 1327, Don Juan Manuel strengthened his position by marrying Doña Blanca de La Cerda y Lara; he secured the support of Juan Núñez, alférez of Castile, and entered into an alliance with Muhammed IV, Sultan of Granada. This formidable coalition compelled Alfonso XI to sue for terms, which he accepted in 1328 without any serious intention of complying with them. War speedily broke out anew, and lasted until 1331 when Alfonso invited Juan Manuel and Juan Nuñez to a banquet at Villahumbrales with the intention, it was believed, of assassinating them; the plot failed, and Don Juan Manuel joined forces with Alfonso IV of Aragon. He was besieged by Alfonso at Garci-Nuñez, whence he escaped on 30 July 1336, fled into exile, and kept the rebellion alive until 1338.

Finally, the Pope brought about reconciliation between Juan Manuel and Alfonso XI. This reconciliation was not complete until 1340, when Juan Manuel and Alfonso allied against the Muslims in the Battle of Río Salado, taking the city of Algeciras. After these events, Juan Manuel left political life and retired to Castillo de Garcimuñoz, where he spent his last years focused on literature. Proud of his works, he decided to compile them all in a single volume. This compilation was destroyed in a fire, with no known copy preserved.

Juan Manuel died at Córdoba in 1348, at the age of sixty-six.