Bruce Banner (Hulk)

Emotional trigger. The transformation is linked to strong emotions, especially anger. Until Banner learned to control this, he was a danger to others.
Destructive Potential. The Hulk's strength is both an advantage and a problem: he can accidentally cause massive damage.
Vulnerable to magic and very powerful technology. In various stories, he was defeated not by brute force, but by cunning, magic, or special devices.

Height and build. In his Hulk form, he is enormous (usually around 2–3 meters or more), massive, and has hypertrophied muscles.
Skin color. Classically, it's bright green. In some versions (especially in early comics), it was gray.
Clothing. Often wears almost nothing: either scraps of a suit or special durable pants designed for transformation.

The Hulk is one of Marvel's most iconic characters, and he has several versions—in comics and in the MCU. I'll cover both to give a complete picture.

Who is he?
The Hulk is the alter ego of Dr. Bruce Banner. Bruce is a brilliant scientist, an expert in nuclear physics and gamma radiation. A botched experiment with a gamma bomb left him exposed to radiation, and now, when under strong emotion (especially anger), he transforms into a colossal green monster with colossal strength.
The Hulk's various "personalities." There were versions: the savage and almost mindless one (the classic green Hulk), the calculating "Grey Hulk" (intelligent, cunning, and acting according to plan), and the "Smart Hulk" (a fusion of Banner's mind and the Hulk's strength).
The crux of the conflict. It's not just "scientist turned monster," but a drama about split personalities: Banner hates the Hulk, and the Hulk often despises the "weak" Banner.

Powers and abilities. Superhuman strength that increases with anger; near-invulnerability; rapid regeneration; leaping vast distances (effectively flying using the force of a jump).