No. 3: General "Thunderbolt" Ross

Credit: Marvel Comics
First appearing in The Incredible Hulk #1 in May 1962, General Thaddeus "Thunderbolt" Ross was there at the Hulk's birth and partially responsible. General Ross was head of the Gamma Bomb project that resulted in the Hulk's creation. A military man, the General has an unyielding desire to safeguard the United States from all threats foreign and domestic. With unlimited government resources at his disposal, General Ross has proven to be one of the Hulk's most tenacious enemies.
Not only does the General battle the Hulk with his military forces, but he also disapproves of Bruce Banner's relationship with Betty, the general's daughter. Combating both Bruce and the Hulk, Thunderbolt Ross has stooped to lows he'd never thought he'd make, allying himself with vile villains such as M.O.D.O.K. and the Abomination, attempting to gundown Banner outright, and even so low as to become the very thing he hates, a crimson hued Hulk himself. Though not an actual villainous person, Ross has been an antagonist to the Hulk since the very beginning.