"The Avengers Battle the Space Phantom"
The Avengers convene in the library of Tony Stark's mansion, and are approached by an alien who knows many of their secrets. Worse, his power is to assume the identity of any individual, and during that time, the victim is prisoner in Limbo. Thus, the Space Phantom strikes the Avengers, sowing dissent in their ranks.
Rick Jones is on hand and discovers the plot, and with the help of the Teen Brigade, informs the others, but not before an all-out brawl among the members of the Avengers takes place. Ultimately, the Space Phantom is defeated, but the fighting has left bitterness in the Hulk's mouth, and he departs, fed up with being on a team. 22 pages (X-435).
First appearance of the Space Phantom.
Reprinted in Marvel Super-Heroes (1967) #1.