Charles I (1500-1558), of the Spanish Empire from 1516, and as Charles V was ruler of the Holy Roman Empire from 1519 until his voluntary abdication in favor of his younger brother Ferdinand I as Holy Roman Emperor and his son Philip II as King of Spain in 1556. The Royal Council was a ruling body and key part of the domestic government of the Crown of Castile, second only to the monarch himself. It was established under Queen Isabella I in 1480 as the chief body dealing with administrative and judicial matters of the realm. With the 1516 ascension of Emperor Charles V to the throne of both Castile and Aragon, the Royal Council came to be known as the Council of Castile because Charles was king of many dominions other than Castile, while the Council retained responsibility only over Castile. During periods in which there was no monarch, an absent monarch, or an incompetent monarch, the Royal Council would rule as a regency council in his place. The Council weakened in the 19th century, where it was abolished and re-established several times before being dissolved permanently.