King Lion-O is the heir to the ThunderCat throne. If he only knew what awaited him, he would remain a baby forever. The young Thunderlord is all grown up, physically and mentally. He now rules Thundera wisely, no longer having the guidance of Jaga's wisdom, Lion-O feels his experience over the years as Lord of the ThunderCats, that he has grown as a Thunderian, a cat, and a leader. Still the most formidable ThunderCat of them all, Lion-O roars on. Although his body needs to be fully developed, his mind is that of a child. He was identical age as the ThunderKittens when they escaped Thundera, but a malfunction in his suspension chamber caused him to age straight through his teens. This means he never truly grew up, but he'll turn into his role as King. The enchanted Sword of Omens and claw shield, Lion-O has power that surpasses those of all the ThunderCats. With Jaga's help, in "spirit" form, Lion-O has learned to trust in the Eye of Thundera, and the Code that binds all ThunderCats. Lion-O knows the meaning of teamwork. When he is in trouble, he can call the other ThunderCats with the sword, by calling them with the ThunderCat signal high in the sky. The sword can also give him "sight beyond sight", so he can see where the danger is about. Lion-O is the son of Claudus the former Lord of the ThunderCats.
King Lion-O leads his ThunderCats in the battle against the monstrous evil of Chime-Ra and his minions of chaos.By using dragon armor invented by Panthro, Lion-O now has three times his own strength and agility, and he's going to need it. The Dragon Wars has been raging for two years and the results, a scorched Thundera and a more aggressive unforgiving ThunderCat Lord. Lion-O means to liberate his world of this threat and restore Thundera to the peaceful haven it was, at any cost.