3. An Intriguing Character
Sentry is an intriguing character because he's generally a good guy but is very easily manipulated. In the picture you see above, he's tearing Ares - a hero - in half, whilst serving Norman Osborn, who got him on side by 'confiding in' Sentry about his own mental issues. Sentry is trapped in a constant battle with his darker side - the Void - and must also constantly use his mental powers to hold his body together, due to its inability to store his vast powers without a conscious, concerted effort. He also, quite literally, can't die unless he chooses to. He's been 'killed' only to reappear alive and well more than once (such as when Morgan le Fay and the Molecule Man killed him on different occasions) and only permanently died in battle with Thor when he essentially asked Thor to kill him - which Thor simply would not have the power to do unless Sentry actively willed it to happen. The ambiguity of the Sentry character, which consequently means he's a constant risk and always teetering on the brink of evil, means that he would be a very interesting character for the MCU Avengers to have by their side.