The Thunderkittens (or Thunderkits as refered to in the 2011 series) are young Thundercats. The most well known ones are Wilykat and Wilykit. Lion-o himself was a Thunderkitten in the first episode, but he is aged into an adult body during space travel.
WilyKit (voiced by Lynne Lipton in original series, Madeleine Hall in the 2011 series) and WilyKat (voiced by Peter Newman in original series, Eamon Pirrucello in the 2011 series) are twin siblings, Kat being the older brother and Kit as the younger sister, both based on the wildcat. They are technically and jointly referred to by the others as "ThunderKittens," although technically they are older than Lion-O. They are the mischief-makers and often have their own lessons to learn alongside Lion-O while they live on Third Earth, where they frequently use tricks and traps to combat evil. Kit is the more adventurous of the two while the older Kat usually errs on the side of caution. Kit also appears to be the more agile, and she employs a rolling-attack against the enemy at times. Their agility is often displayed when they ride their "space boards" — specially designed flying devices shaped like Earth surfboards that can carry them over long distances. Each uses special capsules, balls and other gimmick weapons carried in pouches and on their belts. They sometimes use slingshots to fire these at the Mutants or other foes. They also carry trick lariats, with which they can either tangle and ensnare foes, or use to pull themselves out of danger. In the first episode, they appeared to be slightly older than Lion-O, but when they went into suspended animation, they did not age as far in their suspension capsules as Lion-O did in his.
Thunderian commoners, sometimes referred to has Thunderkittens due to their youth.
- Torr - A young Thunderian commoner, rescued by the ThunderCats along other commoners, from their ship drifting into deep space. Although he was never granted the Thundercat status, he often helped the Thundercats in various missions.
- Leah - A young Thunderian girl, whose escape pod was intercepted by Mumm-Ra and landed in the Jungle of Darkness. Her doll was used by the Ancient Spirits of Evil to disguise the Mirror Wraith to infiltrate the Cat's Lair, forcing her to keep it a secret. She was later freed by the ThunderCats from the influence of the Spirits of Evil.
The Wildstorm Comics introduced two new Thunderkittens
- Wilycat - Son of Cheetara and Tygra, he looks much like his father.
- Wilycub - Son of Cheetara and Tygra, he takes after his mother both in appearance and in his ability to use super speed.
The Thunderkittens often go adventuring alone, as they can sneak into bases through passages that their adult teammates cannot enter.
With other cats
The kittens are still a central part of the team and regularly associate with the other members.
Later when Snarfer joined Snarf, the pair of Snarfs hung out with the pair of Thunderkittens.
The Thunderkittens are featured on the covers of several of the comics: