A 7-page Kirby/Ayers reprint from JOURNEY INTO MYSTERY #79 (1962) leads this collection of reprints. This is a variation on the Jeckyll/Hyde story, with a brilliant but arrogant scientist developing a serum which makes plants and animals immortal, but also makes them huge and monstrous. When his affections are spurned by a young woman he vows revenge, and tries the serum on himself.
For the record, this was originally published the month before HULK #1.
He goes on a cross-country rampage looking for that engineer who he thinks stole his woman, only to eventually fall into a trap, a deep hole constructed by that same engineer, not even realizing that he was being pursued (though you'd think he might have heard from either his old room-mate or teacher, who the monster threatened in pursuit of him, but maybe he actually killed them both between the panels).
Nice short story, both for the variation on the Hulk concept and some of the staging, like the final scene where the monster is falling down the pit.