House of Lara
After the death of his father, Juan Núñez I inherited the title of the Head of the House of Lara and became the preeminent defender of the rights to the throne of the infantes de la Cerda as he had promised Philip of Castile. His principal rival, Lope Díaz III de Haro, Lord of Biscay, became the principal defender of the claims of Sancho of Castile.