Convinced that unaided, the Banner, Green Hulk, and Grey Hulk identities would eventually destroy each other, Doc Samson uses hypnosis to merge the three to create a new single identity combining Banner's intelligence with the Grey Hulk's and Banner's attitudes and the Green Hulk's body. This new Merged Hulk or Professor Hulk considered himself cured and began a new life, but the merger was not perfect, and the Hulk sometimes still considered Banner a separate person, and when overcome with rage the Merged Hulk would transform back into Banner's human body while still thinking himself the Hulk. The Merged Hulk is the largest of the three primary Hulk incarnations. While in a calm emotional state, the Merged Hulk is stronger than Savage Hulk when he is calm. Unlike the Savage Hulk and the Grey Hulk, Banner subconsciously installed a type of safeguard within this incarnation. The safeguard is that when the Merged Hulk gets angry, he regresses back to Banner with the mind of the Savage Hulk.