A subtrope of Token Nonhuman and Token Enemy Minority. This trope is to Token Enemy Minority as Token Nonhuman is to Token Minority. It's about a member of the Villain or Mook race who joins the main cast and their good (mostly human or The Federation) organisation.
There are many reasons for this.
Defector from Decadence: He can't abide the evil ways of his people. Often the result of Klingon [...] [tvtropes.org]