The premier close combat trainer at Sanctuary is a big question mark to most anyone who has met him. His ethnicity, name and age are unknown, as are his motivations for working with Sanctuary. His skill in martial arts, however, leaves most people who meet him struggling to stay on his good side.
Sensei is currently training Mark Simmons in Krav Maga.
Sensei is a metahuman with the ability to instantly assimilate a complex movement into his own memory. In effect, he can learn any martial art by watching someone who already knows it perform the movements. Theoretically, he can learn most any kind of physical activity this way (and probably already has), but he is most renown for his impossibly diverse knowledge of martial arts moves and technical perfection. Sensei is as close as any human has ever come to being a living textbook on close quarters combat.
On the other hand, Sensei does not have enhanced strength, speed or stamina, although he has trained his body to the peak of its natural ability.