Fists is an alien gladiator who fought in the Tri-Sports Arena games.
In the 2003 TV series episode "Turtles in Space, Part 4: The Arena" Fists was ordered by Gruell to fight the turtles in the slave pen, along with Traximus, Monkey Face, Paz, and the Twins. He was ultimately defeated by Donatello. Later in the arena, he was ordered by Zanramon to fight the Turtles to the death, but refused.
Fists also appears as a boss in the Game Boy Advance version of Teenage Mutant Ninja Turtles 2: Battle Nexus.