MODOK, the super-intelligent leader of A.I.M. (Advanced Idea Mechanics) was so convinced that an encounter with the Hulk was inevitable that he decided to create a monster strong enough to defeat the green goliath. The plan required a test subject who was easily susceptible to hypnosis and who had built up enough tolerance to gamma radiation to survive the experiment.
Betty Ross had carried a torch for Bruce Banner long after learning about his transformation into the Hulk. Only after the world thought Hulk was dead did she agree to marry Maj. Glenn Talbot. Soon after the world discovered that Hulk was still alive, Glenn went missing on a military operation. At this time, MODOK turned the emotionally conflicted Betty into the green and powerful Harpy (Incredible Hulk #168).
Firing self-described Hellbolts, Harpy all but killed the Hulk. As Bruce Banner, the hero successfully reversed MODOK's experiment and restored Betty to normal the next issue.