ThunderCats encompasses fantasy and science-fiction elements, it’s a story of good versus evil, it features a mix of magic and technology, hand to hand combat and a central core of championed morals. Its heroes, the ThunderCats, are put up against an assortment of baddies and a demonic wizard called Mumm-Ra on a planet known as Third Earth.
Most of the series focuses on Third Earth as the platform for the ThunderCats’ adventures, however, it is never made clear whether this world is meant to be a future version of our Earth, or an alternative reality or even pre-historic Earth. There are numerous verbal and visual references indicating that there once was an ancient Egyptian culture on Third Earth, hinting that it may be our future world. King Arthur existed in the past of this earth which implies that it is our future world or an alternative one.
The story starts with the destruction of the ThunderCats’ home, the planet of Thundera. Forced to flee their planet, the ThunderCats and their fellow Thunderians board a fleet of starships to escape just as the planet blows up.
Once aboard the fleet’s flagship, a team of ThunderCat nobles gather to protect and escort the sole heir to the ThunderCats’ leadership, the 12 year old Lion-O. The also aspire to safeguard the Eye of Thundera, the source of the ThunderCats’ power, embedded in the mystic Sword of Omens.
Among these nobles is the sage and warrier known as Jaga the Wise. He and the nobles lead the fleet away from Thundera in search of a safe haven. However, the fleet is soon attacked by the Thunderian’s enemies, the Mutants of Plun-Darr, who are looking for the Eye of Thundera. The Mutants attack many of the fleet’s ships and then board the flagship before being driven back by the power of the Eye.
With the flagship low on fuel and severely damaged, Jaga and the nobles decide to head for the closest star system with a hospitable world, but with their navigational systems damaged, one of them must pilot the ship manually whilst the rest travel in suspension capsules. Jaga, the one in charge and the eldest, orders the others to take their places in the suspension capsules whilst he pilots the flagship.
Eventually the flagship nears its destination, however, Jaga’s body is deteriorating due to age, and as he puts the ship on autopilot to complete the last stretch of the journey, his body evaporates into dust.
The ship crashes on the planet Third Earth, its spills its contents aross the landscape, but luckily, the ThunderCats survive. Lion-O and his nursemaid Snarf are the first to appear from their suspension pods, it is soon apparent that Lion-O has aged drastically whilst in the pod. They are soon confronted by the Mutants, who have been looking for them for the duration of their journey and demand the Eye of Thundera from them. Lion-O uses the Sword of Omens to wake the other ThunderCtas, routing the enemies and driving them back in their spaceship.
The ThunderCats start building a new home for themselves on Third Earth from the remains of their flagship, continuing the legacy of their people for upholding Truth, Justice, Honor and Loyalty, the code of Thundera, and protecting the innocent from the evil of the Mutants and the demonic Mumm-Ra vying to possess the power of the Sword of Omens for sinister means.
In later episodes, Mumm-Ra restores the planet of Thundera in order to gain the Sowrd of Plun-Darr which was the cause of Thundera’s demise. He also tries to find the Treasure of Thundera which holds the ThunderCats secrets. The settings for the later episodes alternates between Third Earth and New Thundera.
In the end, the ThunderCats return to Thundera and restore their society, they leave a council of guardians on Third Earth to safe guard the peace of the people on the planet and the whole galaxy.