Ouch, it is Dr.B, and getting him is a pain.
To unlock him, you need to complete Tekken Force Mode 4 times. On the first three, you will gain a Key each time you complete it. By the fourth and final, you will have to fight Dr. B. He fights laying down on the ground, but he's fairly strong, beating him at first time isn't easy.
Hope I've helped, best of luck.
againstall has invadedBECKY = 10/10