Don Martín Cortés y Zúñiga, 2nd Marquis of the Valley of Oaxaca (1532–1589) was the son and designated heir of Spanish conquistador Hernán Cortés by his second wife, Doña Juana de Zúñiga. Don Martín shared his name with an elder half-brother, whose mother was Doña Marina. He was involved with a conspiracy of encomenderos, was investigated, tried, and spared the death penalty.
He was born in Cuernavaca in what is now the state of Morelos. He had an older half-brother with the same name Martín Cortés (1523-1568), son of Hernán Cortés y La Malinche, nicknamed "El Mestizo".
Illegitimate by birth, Doña Marina's son Martín lacked the noble title of don, which his younger, legitimate half-brother held. He also had three sisters: Doña María Cortés y Zúñiga, Doña Catalina Cortés y Zúñiga, and Doña Juana Cortés y Zúñiga. ed "el Mestizo".
According to one modern assessment, "Martín Cortés was everything his father was not.... In place of courage, diplomatic genius, and a talent for leadership, [Don] Martín faced with a straightforward arrogance that he claimed as his birthright."
Don Martín and his brother, Don Luis, traveled with their father to Spain in 1540, to serve King Charles I of Spain and his successor, Philip II of Spain. As a young man, Don Martín became friends with Prince Philips, and both participated in the campaign against the rebellious Low Countries. Through his friendship with Prince Philip, who became Philip II following his father's abdication, Don Martín gained security of title to his estates in New Spain, who "commanded that all the estates and Indian tributaries granted to Hernán Cortés in recognition of his conquests be passed on to his son."
During his residence in Spain, he married his cousin, Doña Ana Ramírez de Arellano, daughter of the Count of Aguilar, Don Pedro Ramírez de Arellano. He maintained close ties with the aristocracy and intelligentsia of the moment, such as the writer Francisco López de Gómara, whom he sponsored to write the biography of his father.