Xander is very shy, quiet, and has horrible self-esteem. He is very unsure of himself in front of people, and tends to remain a strong silent partner behind Moose. Despite his typical fear of everything, he is very deeply caring and compassionate, and will defend his partner Moose with his life.
Xander underwent serious experimentation held captive, being transformed and tested to give humans animalistic strengths. Moose caused quite a bit of chaos and freed him (thus causing Xander's huge attachment to Moose) but not before Xander lost his arms. He does however has a usable animal tail with a working paw on the end, and uses that as a hand instead. While Xander does have an extreme appearance, this is all due to Moose's doing and for Moose's pleasure, as Xander hates to stand out.
This obviously is quite troublesome for him.