Mark is an overly paranoid, possibly traumatized individual. Having encountered 6, an intruder, at a very young age may have left an impact on him growing up. He has some sort of fear of the Torres household for unknown reasoning, whether due to a past experience or simply his exaggerated paranoia is unknown. He tries to speak calmly, and he doesn't have a short temper, but he doesn't trust anyone too easily. He's wary of everyone. His best friend is Cesar Torres.