The House of Haro was one of the most powerful family of Castile during the Middle Age and strongly supported the expansionist policies of Alfonso VI of Castile. As a reward, Íñigo López was named the first Lord of Biscay.
In the early 16th century, the Haro family married paternally into the House of Sotomayor establishing a branch that would go on to hold dominion over the Marquesado del Carpio established in 1559 by King Phillip II of Spain.