The Vegetable is a man who's been a coma since he was 12 years old. Given all this free time, the man who would become the Vegetable spent the next 19 years training himself to become the most powerful mental assassin in history.
He now operates as one of the top mind killers for Brain Damage, Inc.
While the Hulk was occupied fighting Doctor Doom and his gamma-charged animals, the Vegetable infiltrated Hulk's brain. The mental assassin seemingly gained advantage over Bruce Banner's psyche, but the Vegetable was temporarily subdued by the massive Hulk hands coming out of the holes made in Banner's mind fortress. Banner picked up the huge Hulk hands to fight him, but the Vegetable eventually overpowered him. When Banner is about to be killed by the Vegetable, the Hulk appeared, brutally beating the mental assassin to death, thereby saving Banner.