Guilt Hulk

Guilt Hulk is one of the many alter-egoes of Bruce Banner, better known to the world as the Hulk - much as the Devil Hulk embodies all of Bruce Banner's hatred and rage at the world the Guilt Hulk embodies all of Bruce's guilt over the horrors that he has lived through as well as the daily rampages his green-skinned alter ego engages in.

History
Guilt Hulk has resided in Bruce's mind for a long time, alongside hundreds (if not thousands) of other alter-egoes - split personalities formed by his abuse by his father Brian Banner, alongside the Devil Hulk the Guilt Hulk proved to be one of the most dangerous of the alter-egoes and as such was buried deep within Bruce's mind while the Hulk persona tended to keep itself in charge.

However when Doc Samson tried to cure Bruce of his MPD (multiple-personality-disorder) via literally entering his troubled mind he encountered the Guilt Hulk for the first time - at first the Guilt Hulk took on the form of Brian Banner but would soon take on a life of its own following the death of Betty and only via the combined efforts of numerous Hulk personas was the Guilt Hulk stopped from taking complete control over Bruce's mind.