Ryan/Greg/Zack.
Zack Addy is(was) played by Eric Millegan. He's incredibly bright (most likely having Asperger's from what Forensic Antrophologist Temperance Brennan said once) and is very socially awkward. He lived with co-worker and bug guy, Jack Hodgins until the end of season 3. He seemed to have a good relationship with Camille Sayroan, the pathololgist of the Jeffersonian Lab (where the work is done).
In season 3, however, he was the suspect in a cut-off arc (due to WGA strike) about this guy who stole skeletal parts and replaced them with the silver version of that bone piece and kept sending to the Jeffersonian. In the end, it turned out Zack was the Gorgomon's apprentice but Zack plead insane and ended up in a mental facility instead of prison.