ThunderCats follows the adventures of the eponymous team of heroes, cat-like humanoid aliens from the planet of Thundera. The series pilot begins with the dying Thundera meeting its end, forcing the ThunderCats (a sort of Thunderan
nobility) to flee their homeworld. The fleet is attacked by the Thunderans' enemies, the
Mutants of Plun-Darr, who destroy most of the starships in the "ThunderFleet," but spare the flagship hoping to capture the legendary mystic Sword of Omens they believe is on board. The sword holds the Eye of Thundera, the source of the ThunderCats' power, which is embedded in the hilt. Though the Mutants damage the flagship, the power of the Eye drives them back. The damage to the ship means the journey to their original destination is not possible, instead having to journey to "Third Earth"; which will take much longer than they had anticipated. Lion-O's elderly guardian, Jaga, volunteers to pilot the ship while the others sleep in capsules; however, he dies of old age in the process, but not before ensuring they will reach their destination safely. The flagship contains the young Lord of the ThunderCats, Lion-O, as well as the ThunderCats Cheetara, Panthro, Tygra, WilyKit and WilyKat, and Snarf.
When the ThunderCats awake from their suspended animation on Third Earth, Lion-O discovers that his suspension capsule has slowed rather than stopped his aging, and he is now a child in the body of an adult. Together, the ThunderCats and the friendly natives of Third Earth construct the "Cat's Lair," their new home and headquarters, but before long, the Mutants have tracked them down to Third Earth. The intrusion of these two alien races upon the world does not go unnoticed, however - the demonic, mummified sorcerer,
Mumm-Ra, recruits the Mutants to aid him in his campaign to acquire the Eye of Thundera and destroy the ThunderCats so that his evil might continue to hold sway over Third Earth.
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