It has been implied that Hulk can’t be killed, yes. There is a story called The End, where he is the last sentient being on Earth being followed around by a robot waiting for him to die so he can record it.
It states clearly that he cannot die, and also that he will not (or cannot) change to Banner, because he is so old that Banner would die. Obviously, this is a future possibility, and not canon, but it certainly shows that this is a possible chance.
It has also been mentioned, maybe just as a theory, that Hulk is a manifestation of Banner’s survival instinct, rather than his anger. This goes along with that story, and also explains why when Banner has tried to commit suicide, he turns into Hulk without trying. It also goes along with the fact that She-Hulk is linked to fear, as fear and anger are linked, both responses to potential threats.
All of which implies that it could be impossible to kill Hulk. However, it is certainly possible to defeat him.
Yes, the Hulk has been defeated on several occasions including but not limited to:
- Defeat by the Silver Surfer via his use of the “Power Cosmic” to drain the Gamma radiation from Hulk’s body reverting him to Bruce Banner
2. Almost killed by Silver Surfer via the Power Cosmic
3. Knocked out and almost killed by Thor via a blow from Mjolnir
4. Knocked out by Thor via lightining
5. Beaten to a pulp by Zeus
Alternate Future timeline or universes also have Hulk being killed quite often such as by King Thor
And by Deadpool
Main canon Hulk has actually been “killed” multiple times (but brought back to life)
