He is the evil counterpart of Jake Long. He is accidently created by Jake and attempts to take his place by absorbing his chi energy. He only appears in the episode "The Doppelganger Gang" in Season 2 and never makes another appearance.
In "The Doppelganger Gang", Jake learns the benefits of splitting his chi energy into perfect copies of himself, which are called Doppelgangers. But, when Brad challenges Jake to a fight, Jake attempts to make another clone to take the hit in his stead. However, Jake inadvertently uses a negative chi amplifier that causes the new Doppelganger to be 100% evil, hence creating Yang Jake.
Yang Jake looks exactly like the original Jake, but with slightly darker colors. The evil doppelganger eventually goes on to absorb the other Jake doppelgangers in an attempt to overpower the real Jake. In the end, Jake reabsorbs Yang Jake as negative ch'i, possibly destroying him. It is not known if Yang Jake will make any future reappearances. Although called Yang Jake, he is never referred to Yang Jake in the episode. Instead, Jake calls him "Evil Jake".
- The Doppelganger Gang (first appearance)