Not much is known about Xander, what little is known suggests he was confined for most of his youth and experiemented upon, he now seeks retribution. He is a superhuman much like Alex, but the limits of his abilities are currently unknown. He now serves as a member of Carter's squad.

But he seems to be hiding an ulterior agenda..

He is tranquil yet subtely sarcastic and speaks in a very silky-smooth and respectful manner. Though he can sometimes have his head in the clouds, and let his lack of experience affect his attitude.

An example of his voice can be heard at 1:13:08 of this video, during a conversation:

https://www.youtube.com/watch?v=FNxRY-75kco