Charles V
Charles V (Carlos) was Holy Roman Emperor and king of Spain (as Charles I).
History
Charles was the eldest son of Philip and Joanna, daughter and heir of Ferdinand II and Isabella I. Importantly though, Joanna never reigned herself; as long as he lived, Ferdinand restrained her from court and ruled Castille in her name.
Charles' grandfather, Maximilian I, was Holy Roman Emperor.
Following his father's death in 1506, he succeeded as duke of Burgundy. Then in 1516, following his maternal grandfather's death, he usurped his mother to become king of a unified Spain. He was enumerated Charles I as such. Finally, following the death of his grandfather in 1519, he was promptly elected as the next emperor.
Charles largely decentralized the empire. He appointed his brother, Ferdinand, to manage Austria in his name. He also saw to Ferdinand's election as king of Germany in 1531, declaring him as heir apparent.
Most of his reign was focused on suppressing religious conflict within the empire and the Burgundian realms, whicha t this point were fast dissintegrating into
Charles declared intent to abdicate in 1556. He divided the empire between Ferdinand and his son Philip II, with Spain and the entire colonial empire going to the latter. This created the split between the Austrian and Spanish Habsburgs.