The ThunderCats were a group of Cats from an unknown planet, who landed on Third Earth at the time in which Mumm-Ra the Ever-Living was overthrown by none other than the ThunderCats themselves. The Order of the ThunderCats has existed for thousands of years, and the legacy continues with the current lord of the Thundercats Lion-O, who once again will overthrow Mumm-Ra, as the Original Thundercats have done in the past.