When a young biochemist injected himself with a new Super-Soldier serum and then crashed his car into a swamp, he is transformed into a slow-moving, red-eyed plant creature who saves babies and defends the swamp (and the magical nexus located within). By what name is he known?

Man-Thing is the correct answer - his origin exactly matches this description. Biochemist Dr. Ted Sallis injected himself with a Super-Soldier serum variant, crashed his car into a swamp, and was transformed into the slow-moving, red-eyed plant creature Man-Thing. He protects the swamp and the magical nexus within it, and is known for saving babies. Swamp Thing (DC), The Heap, and The Thing (Marvel's Ben Grimm) are all different characters.