Lope Díaz IV de Haro

Lope Díaz de Haro (b. ? - d. October, 1322) was a Spanish noble of the House of Haro, the traditional Lords of Biscay. He was the firstborn son of Diego Lopez V de Haro, Lord of Biscay. Whilst he did not inherit his father's title of Lordship over Biscay, he is best known for being the lord of Orduña-Urduña and of Balmaseda. He further served as Alférez to King Ferdinand IV of Castile.

Lope Díaz IV de Haro was the son of Diego López V de Haro and his wife, the infanta . His paternal grandfather was Diego López III de Haro and his wife, Constanza de Bearn. His maternal parents were King Alfonso X of Castile, King of Castile and Leon, and his wife, Violant of Aragon, daughter of King James I of Aragon.

As the firstborn son of Diego López V de Haro, Lope Diaz IV was raised believing that he would inherit the Lordship of Biscay. After a lengthy series of disputes over the succession to Biscay which often turned violent, the title passed to María II Díaz de Haro, daughter of Maria II Diaz de Haro, Lope Diaz' cousin.

With the death of Lope Díaz III de Haro who was assassinated by order of King Sancho IV of Castile in 1288, the title over Biscay passed to María II Díaz de Haro being the eldest child. After the ushering in of a new infant king Ferdinand IV of Castile after Sancho IV's death, the kingdom was thrown into chaos and Diego López V, Lope Diaz IV's father, was able to forcibly take control of Biscay away from his niece whose husband, the infante John of Castile was imprisoned at the time for crimes committed against Sancho IV in collusion with Diego Lopez III de Haro. This led to a lifelong fight between the two parties and a struggle to gain favor with the royal court, both sides having been at times considered at war with the crown.

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