The Hulk was created by
Stan Lee and
Jack Kirby in 1962.
The Hulk's alter-ego is Robert Bruce Banner. Originally, it was
just Bruce Banner, but Stan Lee kept forgetting his name and
called him "Bobby" in one of the comics and hence, Banner's first
name was born.
When the Hulk first appeared, he was not the green incarnation that
is well-known today, but actually he was grey and more intelligent
than he later was. The Hulk's initial transformations were triggered
by the setting sun, but later Banner only transformed when under
stress or danger.
The Hulk and his multiple incarnations have, in recent years, been
tied to the fact that Banner suffers from Multiple Personality Disorder
with the Hulk being an outward manifestation of those personalities.
Hence, the Hulk has been green and child-like, green and highly-
intelligent, green and savage, grey and devious, etc. Ultimately,
this shows that Bruce Banner is one of the most mentally unstable
of the super-heroes.