One of the long forgotten characters of Sega Team, Nack the Weasel first appeared on Game Gear Game "Sonic Triple Trouble", then in another Game Gear Game called "Sonic Drift 2" And also in a fighting game for the arcade machine Sega Model 2 called "Sonic the Fighters".
According to the manual, he comes from the Special Zone, and that's why he has 4 fingers on his hands instead of 5 like Sonic or Tails (at least in the classic version) and he is also a hybrid species, a wolf - weasel, possibly where his japanese name comes from "Fang the Sniper".
He looks like a cute chubby weasel, but he is really a bounty hunter, always looking to do stuff in exchange for money.
This drawing is a traced (vectorized) version I made from the Sega artwork for the games, that I also used as reference to make this balloon art: http://www.furaffinity.net/view/16969862/