Knuckles The Echidna

Knuckles The Echidna is the tritagonist of the Sonic The Hedgehog franchise originally making his debut as the (former) secondary antagonist of Sonic The Hedgehog 3 and its continuation Sonic & Knuckles where he is tricked by Dr. Ivo Eggman Robotnik into thinking that Sonic and Tales are evil until he steals the master emerald making Knuckles realize otherwise. It was from that moment that he became an ally to Sonic and Tales. However despite this he was also the secondary antagonist of Sonic Triple Trouble where he was working for Dr. Robotnik once again.