Frederick III (1415-1493), also known as Frederick the Fat and Frederick the Peaceful, was the eldest son of the Inner Austrian duke Ernest the Iron, a member of the Habsburg dynasty. He became duke of Inner Austria in 1424 at the age of nine, but would not rule until 1435, with his younger brother Albert asserting his rights as co-ruler. By 1439, Frederick had become the undisputed head of the Habsburg dynasty.