Jack Jenie is a Geniosapien. He first appeared in Just Ben. He is a villain.
He looks a little like Ben 10,000, but without the beard and different hair. His hair color is black and he has orange skin. He has green eyes with no pupils. He wears clothes similar to Ben 10,000 also.
He is not very cruel and cold-hearted, unlike other villains Ben has faced. He is not all that intelligent either, as he doesn't know much about the Omnitrix.
Jack first appeared in Just Ben, tricking Ben 10,000 into saying he never wanted to be Ben 10, which makes them go back to the past and Jack ends up with the Omnitrix instead. he is later defeated by Ben, Julie, David, and Jonah, which results in Ben getting the Omnitrix back and later the Biomnitrix. He later says he'll get revenge on Ben, and then the episode ends.
The only power he is shown to have is the ability to grant wishes.
Jack appeared to not have knowledge of the Omnitrix, which led to him being defeated.