When dangerous radiation levels mysteriously contaminated parts of the ocean, Prince Namor returned to the Earth's surface to seek help from scientific genius Reed Richards (a.k.a. Mr. Fantastic). But the preoccupied Atlantean wasn't quite himself. Although he recognized Hulk when they crossed paths on the street, only after a memory-jogging conversation with Nighthawk did Namor recall that he had once been a member of the Defenders and agree to accept their assistance instead (Defenders #52).
The Defenders last saw the Prince of Atlantis when he came to the aid of Nighthawk in Giant-Size Defenders #3. But what had he been doing ever since?
During that interim, Giant-Size Super-Villain Team-Up #1-2 and Super-Villain Team-Up #1-13 featured the unlikely pairing of Prince Namor and Dr. Doom, ruler of Latveria. Reasoning that he needed the help of another monarch to successfully overthrow the rest of the world, Dr. Doom had tried to both entice and coerce Prince Namor in assisting him.