Diego López IV de Haro

Diego López IV de Haro (died 1289) was a Spanish noble and the Lord of Biscay from 1288 to his death in 1289.

Her maternal grandfather was Gonzalo Núñez de Lara, señor of Belorado.

Diego López joined the side of Navarre and Aragon supporting the pretender to the throne Alfonso de la Cerda in the larger conflict to fight against Sancho IV of Castile.

The war went poorly for Diego's side as the forces of Sancho IV began taking large swaths of territory, including the towns of Labastida, Orduña-Urduña, and Balmaseda.

As a result, there were a series of disputes as to the succession of the lordship title which eventually passed to María II Díaz de Haro.