For the new 2011 version, see Lion-O (2011 TV series). Lion-O (voiced by Larry Kenney) is the son of Claudus, and is the leader and hereditary “Lord of the ThunderCats”. His adventures are shown from childhood to adulthood on Third Earth and New Thundera, together with his friends and followers, the ThunderCats. At the beginning of the series, Lion-O is a boy of mere twelve years old. He was among the group of Thunderian nobles to make the trip to Third Earth in the flag ship of the Thundercats,