Fernando I was a king of Castile and Leon in the 11th century, known for his efforts to unify the Christian kingdoms in the Iberian Peninsula. He ruled from 1037 until his death in 1065 and was instrumental in expanding his territories through military campaigns against the Muslim states in the region. He is also recognized for his role in the establishment of the Spanish monarchy, as he was the first to hold the title of Emperor of all Spain. His reign laid the groundwork for future unification efforts, influencing the political landscape of the region for generations to come.