"He's like the teammate none of them are sure they want on their team," Hulk actor Mark Ruffalo joked, when describing his character's role in The Avengers. "Loose canon" would be one way to describe scientist Bruce Banner, but another would be that he has a split personality that manifests as a goliath, green monster. The worst part of the ability is debatable; Banner often has absolutely no control of when and where he changes into the Hulk, but anger famously sets off the transformation. The Hulk shows no respect or care for anything that Banner does or loves: it's possible that Bruce's alter-ego can destroy whole cities in just one burst of anger. The scientist lives in constant fear of the monster inside of him; it's like Jekyll/Hyde, or a werewolf, but capable of the apocalypse. Whilst Banner/Hulk is a fascinating study of human nature verses the darkness within our psyches, it would be hell to actually live with. There's a reason that Bruce Banner never actually leads the Avengers: he often involuntarily loses all sight of morality, just becoming the most destructive force on the planet: it's an ability that few have envied.
