Cartoon Intros

A classic battle between good and evil set in a time that combined high technology and hand-to-hand combat. The Thundercats are humanoids with distinct feline appearances, while the Mutants (bad guys) are a rag-tag group of uglies.

Throughout most of the series, the action is set on a planet called "Third Earth", a future version of our Earth.

Both the Thundercats and the Mutants are non-natives. The ThunderCats fled their home planet, Thundera, as it was being destroyed by the Sword of Plun-Darr's magic; and the Mutants from the planet Plun-Darr pursued them, seemingly annihilating all ships and their occupants (the entire remaining population of Thundera) except for the flagship, which contained the Sword Of Omens, an artifact the Plun-Darrs desired. They fail to fight the now combat-ready ThunderCats and are driven back. They decide to travel to the nearest system with a hospitable planet. They enter cryopods, except for one who stays back to pilot the ship during the long trip. The ThunderCats bring to Third Earth their code of Truth, Justice, Honor, Loyalty, which threatens the evil dominion of Mumm-Ra, an ancient devil priest of First Earth.

The Mutants and Mumm-Ra seek to possess the magic Eye of Thundera, the source of the ThunderCats' power, embedded in the hilt of the mystic Sword of Omens. The battle for ownership of the Eye fuels the conflict between the ThunderCats and their enemies at first; but eventually, the Mutants and Mumm-Ra want nothing more than to retake Third Earth in the name of evil and do away with the ThunderCats entirely.

In later episodes, Mumm-Ra magically reconstructs Thundera in order to gain the Sword of Plun-Darr and locate the Treasure of Thundera, which harbors the ThunderCats' secrets. In these episodes, the ThunderCats' adventures alternate between New Thundera and Third Earth. Eventually, the ThunderCats return to New Thundera to rebuild their society, while still maintaining guard duty on Third Earth.