Small in stature but large in bravery, the young Lord Lion-O is the hereditary Lord of the ThunderCats. Still lacking in skills and wisdom due to his young age, Lion-O nonetheless displays many of the raw qualities needed to prove himself as a fine leader of his people. Lion-O is shocked and devastated by the destruction of his home planet Thundera, and the trauma of its destruction is something he will carry with him into adulthood, but, in-keeping with his headstrong nature, this will not prevent him from leading the ThunderCats to a new and happy life on Third Earth.

Exodus

Unaware of the chaos going on around him, The young Lion-O slept peacefully aboard the Thunderian flagship which flew away from his dying home planet of Thundera. He was awakened by Cheetara, and despite his nursemaid, Snarfs, objections, he went to the bridge at the request of Jaga. There he witnessed the destruction of his home, and was shown the mystic Eye of Thundera by Jaga, as well as the Sword of Omens. When the Mutants attacked the ship, Lion-O remained in the sword chamber, where he was eventually found by S-S-Slythe and Jackalman, Lion-O barely had the strength to lift the sword of omens, but he eventually managed to, and the eye of thundera saved the Thundercats by driving the Mutants from the ship.

Lion-O then sadly bid farewell to Jaga as the Thundercats entered their suspension capsules.