The Sentry is the strongest Avenger, whose laundry list of incredible abilities make him a serious threat to whoever he's facing. Even when matched up against a literal god, the Sentry has come out on top - as he once ripped Ares in half after his bad side started to show.
The Sentry first debuted in The Sentry #1 by Paul Jenkins and Jae Lee. Bob Reynolds was a pudgy, depressed man who secretly had a nearly immeasurable amount of power after being injected with a serum that gave him the "power of a million exploding sons." While he had a deep history with the Avengers, there was a bad side of the Sentry called the Void. In order to stop the Void from taking over Reynolds and becoming a nearly unstoppable supervillain, the Sentry wiped his own and the entire world's memories of him. Later, the Sentry would return and has been both a good guy and a bad guy, as the Void dictates his allegiances.
The Seige storyline saw Norman Osborn become the Iron Patriot and attempt to take out the original Avengers. The Sentry would fight alongside Norman and aided him in his effort to take down Asgard. After successfully bringing chaos and destruction to the floating city, Sentry goes one-on-one with Ares, the God of War. While fighting a god would be difficult, the Void starts to creep through during the match which leads the Sentry to grab his body and rip it into pieces. It's one of the most gruesome scenes that Marvel Comics has ever published. (Violence Warning)
Ares's brutal death shows why it was so important that Reynold's memories were wiped from his mind in the first place. He doesn't have control of his immense powers and while he can be a helping hand to the Avengers, when the Void shows its ugly face, there's no telling what kind of damage it can do.
After taking down Ares and Asgard, the Avengers find a depowered Reynolds in a giant crater in the ground. When he awakes, Reynolds asks "did, uh, did I do this?" and begs the Avengers to kill him. Thor wants him to pay for his crimes but won't kill him. But, the Void reemerges and attacks the superteam. Thor is forced to kill him and throws his corpse into the sun. While the Sentry would eventually be revived, the arc showed just how powerful Reynolds is when he doesn't have control - taking him down is next to impossible, even if you're a god.
