Anthrax (1987)

Antrax is a character from the 1987 cartoon and toyline. He looks like a giant ant wearing an executioner's hood and outfit, and armed with an appropriate axe. In both the toy and the show he's labeled as "Krang's executioner from Dimension X", which makes him an alien rather than another mutant. He appeared once in the 1987 cartoon episode "Night of the Rogues" where Shredder hired some of the Turtles' past foes (including the Rat King, Leatherhead, Slash, Tempestra, Chrome Dome, and Scumbug) in hopes of defeating the Turtles. Oddly enough, while this was the first appearance of Antrax and Scumbug, April and the Turtles acted as if they encountered them before.

Trivia:

 * It is possiple they may have met Anthrax back when they were in Dimension X.