He is often described as being a spitting image of his mother as he has red fur but unlike most foxes or vixens he has full red fur like the Peruvian general Alberto. In the Bunker he wears a white T-Shirt, black trousers and a black jacket like a suit jacket, outside the Bunker he adds a dark green waterproof coat but he wears his suit jacket in Argentina. His clothing listed is only on formal occasions in the Bunker whilst in general around the Bunker he wears his T-shirt but instead of wearing canvas trousers like most of the older boys in the Junta he wears jeans.
Like his sister Jacqueline Marco likes the Junta babies Josefina and Santiago but unlike his sister he manages to hide his emotions which earns him the respect of many older children in the Junta because as Hugo puts it 'Some children would find the babies innocent. It takes a special fox to hide his emotions to them' He's caring but has fits of silent aggression and often comes off as being very cold and mysterious.
One frightening aspect about Marco is that he is able to crush his sisters feelings of wanting to kill the babies at night because of either Josefina, Santiago or both screaming and crying at night and making her lose out on sleep and how he manages to sleep at night whilst his sister is always awake because of the babies screaming and crying. Though he enjoys the humiliation of the former Junta torturers Olivia and Rachel he later sympathizes with them after their second release and the same goes for other female members of the former Animalian Junta. He may seem cruel because he at one point considers stripping Olivia and Rachel completely and putting them in nappies but decides against the idea saying "We may be humiliating them. But there is a difference between humiliation and degrading. Putting them in nappies is a sincere example of degrading" Though he finds putting them in nappes degrading he has no problem with treating the torturers like slaves just as other female members of the Junta do to other prisoners. But aside his dark and cold personality he loves his sister and has friendships with other older boys in the Junta