(älvä'rō dā lū'nä) , 1391?–1453, constable of Castile, grand master of the Order of Santiago. The favorite of John II of Castile, he virtually ruled the kingdom, winning victories over the Moors (1431) and the rebellious nobles (1445). However he aroused the enmity of John's second wife, Isabel of Portugal, whose schemes led to Luna's trial and execution.