The Hulk obtained his powers from gamma radiation.
In Marvel’s classic origin, scientist Bruce Banner is exposed to the blast from an experimental gamma bomb while saving teenager Rick Jones. The radiation alters Banner’s body and triggers his transformation into the immensely strong Hulk, especially when anger or stress overwhelms him.
The Hulk first appeared in Marvel Comics in 1962, created by writer Stan Lee and artist Jack Kirby. He was initially depicted with gray skin, but printing difficulties led Marvel to change the character’s color to green, which became his defining look.
Other Marvel characters, including She-Hulk, the Leader, Abomination, and Red Hulk, also have gamma-related origins. That broader group can make the wording seem less exclusive, but Hulk is the singular, canonical answer to this question. In real science, gamma radiation is highly energetic ionizing radiation and does not produce superpowers.