Francisco Javier Castaños Aragorri, 1st Duke of Bailén (24 September 1758 – 22 April 1852) was a Spanish Army officer and politician who served in the French Revolutionary and Napoleonic Wars. He presided over the Regency Council of Spain and the Indies (de facto head of state), in 1810. From July to September 1834, Castaños served as the first president of the Senate of Spain, at that time called the House of Peers.
Castaños is remembered for his victory over the French under Dupont, whom he surrounded and compelled to surrender at the decisive Battle of Bailen in 1808, where the Napoleonic army was defeated in the open field for the first time and which led to King Joseph having to abandon Madrid at the end of that same month. Just months later he led his army to a decisive defeat at the Battle of Tudela. After this he served under Wellington in several engagements, and was commander of the Spanish army, if required, to invade France in 1815.