Timestopper

A fourteen-year-old delinquent with a clock in his chest, and the mechanism is specified more carefully than almost anything else in this show.

The clock counts down from ten, then freezes one Limbo minute of time. He chooses what gets frozen, and frozen things render grey, so the animators get to show the power working without spending a line of dialogue on it. If he fails to restart time, the clock explodes. His stated weakness is fear of the dark, and the clock will not work in total darkness at all.

He joined the Mob after the breakout of 2839, and he did it by stealing the Road-Star out from under Mo-Lec-U-Lar and Mumbo Jumbo, which impressed Mon*Star enough to hire him. Eight appearances are on record. The oddity worth keeping is that despite full membership he is missing from both of the big Mob roll-call episodes, The Blue Door and Airshow.

Voice. Wikipedia and thundercats-ho.fandom both credit Larry Kenney. The ThunderCats wiki leaves the field blank, so the two sources that guess agree and the one that usually cites timestamps abstains.