Many have tried but few have ever succeeded.
Marvel's green giant, The Hulk, just isn't something that can easily be killed. Based on overall strength and hard-to-kill-ness ability, the muscled meanie is Marvel's best bet against DC's Superman. He can smash others easily but rarely the other way around. Iron Man and Wolverine have tried. They couldn't finish him.
Guess who did, though. Guess who finally sent the Hulk to Gamma-heaven.
Yes, the much-maligned arrow-guy who's severely underqualified in a group featuring a Norse god, a cosmic sentinel, and various other superhumans. The unthinkable happened in Marvel's Civil War II (issue #3 of seven) where Hawkeye sent an arrow flying through Bruce Banner's skull.
So there you have it. An arrow killed The Hulk. Not Iron Man's fancy toys. Not Wolvie's adamantium claws. But human Hawkeye's arrow.
Now, the more interesting question is, why would he do that? A character known as Ulysses (an Inhuman, a human-like race in Marvel with advanced abilities due to genetic manipulation) saw in a vision where Hulk killed off a number of Avengers. In order to avoid the scenario, Banner himself allegedly asked Hawkeye to kill him off. He even gave Hawkeye the anti-Hulk arrow that will finally kill him.
And thus ends the life of Hulk...for now. Of course, this is the world of comics where heroes and villains alike have a hard time staying dead.
If you're sad, know that there's another Hulk around. He's in The Totally Awesome Hulk series, where, in his human form, he is a Korean-American teen genius named Amadeus Cho. He had apparently absorbed Banner's gamma radiation in the series, thereby transferring the iconic behemoth's abilities to him.
Image via Slashfilm.com