Coyote

From Shadow Unit Wiki

Coyote is a nickname for Chaz Villette. Presumably, it comes from his caged-coyote mannerisms.

Chronologically, the first reference is by Esther Falkner in episode 1x01, "Breathe":

How many New Kids had she seen? In the army, then as Supervisory Special Agent? They dealt with it however they had to, but you never knew who they were until they quit dealing with it and relaxed into the job. Brady had arrived buttoned-up, stone-faced, and professional. Lau had worn a flawless PR glaze, as if life were a press conference and her future depended on holding a measured smile. Chaz had shown up in an ill-fitting navy-blue suit and and a painfully fresh haircut, moving like a coyote trapped in a pet carrier. [1]

Chaz uses various coyote pictures for most of his LiveJournal userpics, along with one of Wile E. Coyote holding up a small "Yikes!" sign.