Maegor I Targaryen, King of the Seven Kingdoms

From Asoiaf

Maegor I of House Targaryen, King of the Seven Kingdoms (reigned 42 Al - 48 AL), called the Cruel was the son of Aegon I Targaryen, King of the Seven Kingdoms and Visenya Targaryen.

He succeeded his half brother Aenys I on the throne.

On his death, his nephew Jaehaerys I became king.