Constable of Castile (Spanish: Condestable de Castilla) was a title of a military nature created by John I, King of Castile in 1382, as a result of the Third Fernandine War against the Portuguese and the English.
The post substituted the title of Alférez Mayor del Reino and was more consistent with that of the French Constable of France. The constable was the second person in power in the kingdom, after the King and had supreme authority over the Army, as well as broad jurisdictional powers.
In 1473, Henry IV of Castile made the title hereditary for the Velasco family and the dukes of Frías. By that time, the position lacked any substance, and therefore it was decided that the title would cease to have any military or administrative connotations, and was simply an honorific title.