Well, first of all, there's Bruce Banner, the scientist. His work with gamma radiation is crucial. Then, the accident that exposes him to the gamma radiation is a key part. And of course, the transformation into the Hulk. The Hulk's appearance - big, green, and super - strong - is also an important element. Also, the fact that the transformation is often linked to Banner's emotions, especially anger.
In the Hulk comic book origin story, the main elements start with Bruce Banner's character. He's a smart yet vulnerable scientist. The gamma radiation experiment he was involved in is central. The accident during this experiment that bathed him in gamma rays is a turning point. After that, the transformation into the Hulk, which is not only a physical change but also a change in his mental state. The Hulk has a more primal and aggressive personality compared to Banner. And the continuous struggle of Banner to either control the Hulk or find a way to reverse the transformation is also a significant element throughout the origin story.