Leader is is a member of the Inuwashi Gunjin a race of winged eagle like aliens who hold a samurai like code of honor, him and his brethren were were enslaved by Darius Dun , who laid them in shackles and kept them in freezer capsules until they were needed, and used as assassins. Despite this humiliation the Gunjin kept their free will and their sense of honor. As the Turtles in one of their missions protected Cody against Leader and his fellow Gunjin even at the risk of their own lives, sensing the turtles honor Leader and the Gunjin finally rebelled against Dun and helped the Turtles to bring Cody to safety. When their bands were destroyed, they finally gained their freedom. In the episode The Cosmic Completist Leader returns and finds himself in Cody's apartment requesting the turtles help to find his fellow Gunjin who were kidnapped by an alien collector Aramzedo who wanted Leader and his fellow Gunjin to his collection of rare life-forms. After he teams up with the turtles he frees his brethren and defeat Aramzedo. The Gunjin take charge of Aramzedo's ship and ensure the Turtles that they will make sure everyone is taken back to their homeworld. The TMNT are worried that the task is too daunting, but Leader explained that Aramzedo will help them in return for his own freedom.