I had this at the back of my mind, and the partial opening I saw seem to confirm it. The leader of the secret conspiracy is a brilliant, great leader, a true leader-THE LEADER! Having had secretly another underground lab, which had the ability to recreate itself, it created a body for the Leader to allow for his return. What he saw once past death left him shattered, and more convinced than ever that good is a fools game and that in serving evil, he is serving the only cause with anything in it. He found out about a conspiracy in the US, and became its head...secretly. By 'converting' those high enough to be safe from investigation. The reason for the conspiracy is simple; What is the essence of the Banners power? He with a few others is able to absorb energy out of radiation. For him, radiation can be a feast. Banners DNA, could make World War III thinkable! And render the US the outright winner; a race of hulks emerging on a bombed out earth, the free floating radiation making them stronger and stronger-like the Maestro. Of course, the core of the Hulk is Banners mental state-so to find ways round that they need plenty of DNA, and after the She-Hulk it seems that blood transfusion is a realtively safe way of injecting the Banner increment. I therefore suggest the conspiracy has been in existance since it was revealed that Banner was the Hulk, and the nature of his creation-and due to the nature of the cause, they have allies everywhere, possibly in other countries. The Leader is the only terran superhuman who has been able to beat death fully. Im suggesting that he lost his Deus Machina, BUT he had another method in mind. Using 'converted' people he managed to steal Bettys body, and then began 'rebuilding' her. In the words of the Black Panther, she is Betty Ross-but she is not the same Betty Ross, She is not the same as any woman who ever lived. The Leader wants to string out his fight with the Hulk this time. Not to risk fighting him openly-that way hell lose, like aways. Force the Hulk to fight-his way. Those people were speaking the truth. The leader wanted them to. To "Help Dr Banner..." into his grave.
Theory by NeroDart (Thanks for your contribution!)

The assumption was that the Professor was the Merged Hulk. Right; during the final battle with Onslaught, the Professor urged the X-Men's nearby telepath (Jean Gray) to switch off his intellect so he could access the unmeasured strength of the Savage Hulk. This created the lesion-supposedly, that allowed, when Onlslaught fell, and Earth's heroes were drawn into the Franklinverse, for Banner to be split from the Hulk, and allowing him to be incarnated in the Heroes Reborn cosmos, leaving a Bannerless Proffessor; and it was this void at his center that caused him to go wild and... Slowly sicken. When they merged, again the shock, the pain... Banner's relived memories made the Professor for a time become slightly... Out of it. But the professor was NOT the Merged hulk, and not a cured Banner. So... When Banner's intellect was switched off, it was ONLY the Proffessor who was switched off. Since he was not the merged Hulk, things returned to their... Familiar status quo. So it was easy in a sense to see Banner as separate from the Hulk. After that, the Proffesor was returned. But Banner was gone. Remember-The Proffessor was a perfected version (ideally) of Banner. A perfect reflection. But the face he was reflecting... Was no longer there. He was hollow. Slowly caving in. Since being split from Banner has never been a good idea, the Hulk began to sicken. This was slowed by the energy he was receiving from the Heroes Reborn universe. But that only went so far. The Professor no longer had a core. Without it, without his purpouse, he began to cave in emotionally, and in the end develop VERY un-Hulk like traits like despair. Fortunetly, he was saved by the return of Banner. There was the pain, the agony of Banner's remembered past... Also, Banner wasn't quite Banner anymore. He had been changed by his time in the HR universe. There were some differences that made the fit, no longer as comfortable as before. But in the end, it quietened down, and might have worked. Then Betty died... Temporarily. The pain triggered the slow collapse of the Proffessor... And since the Professor was NOT a Merged hulk, the Savage Hulk, and the Grey Hulk were able to emerge again.
Theory by NeroDart (Thanks for your contribution!)

The Mindless Hulk has no reaction. He has rage, but it only goes so far. His mind is limited to the immidate and concrete. The Savage Hulk is the ultimate child... He has a mind... Of sorts, but a mind dominated by emotion. BUT, he has some sort of mind. A space where emotions can grow. True, his 'logic' seems to do little more than fan his fury... But that's the point. The Savage Hulk's emotions can just grow and grow. As his need grows and grows, the Mindless Hulk is limited, and can be drawn off by immidiate pleasures... "YOU KILLED HULKS FRIEND! YOU KILLED HULKS FRIEND! HULK WILL SMASH YOU ALL!" You could see this as slightly religiously; Banner as the everyman ego; limited, weak, but wanting good and wanting good to triumph. The Savage Hulk; the wanting, trusting child... The 'nice Adam'. The Grey Hulk; the human ego; or perhaps a bit of the old Adam; self seeking, limited in vision. Perhaps now and then seeking good, but unable to see past his own needs...
Theory by NeroDart (Thanks for your contribution!)

On the variations in the Hulk... I'd suggest that in our universe, rather than the Heroes Reborn universe, the Grey Hulk emerged first from the simple fact of the balance of forces inside him. This couldn't last long: The repressed child side was simply too strong, too elemental to be held back forever. The first sign of this change is that for some time, even though the Grey Hulk's persona was in control, his skin was green. I'm assuming there was a slight but substantial increase in power for the Hulk: As in the early Avengers Hulk. There was also a period where the Hulk was the mind slave of Rick Jones. I'm assuming that the radiation Banner absorbed in space altered him, causing the change in the Hulk's transformation pattern, and speeding up the emergence of the Savage Hulk. This, along with the shock that they both had created a primitive mind link between the two. In the meantime, Banner on the craft, began to turn into the Hulk again, and for the first time, mentally gave in. He saw his situation as hopless, and went into a sort of amenisiac state, an escape into black. This, given the nature of his state, took a little while. But when the Hulk and Rick faced off on the mountain, it was almost complete, it was ended when, without knowing it, Rick called on that link. Due to the fact that Banner's selves are physically incarnated, the escape into black became visible, its effects and features. The Hulk became a living Zombie, under Ricks control. But the Hulk's rage, amplified by its repressed knowledge of its slave state, couldn't be contained. The Zombie Hulk's strength levels were upgraded by the absorbed radiation. He also gained, probably connected to the mind link, the power of flight, which was essentially a new but temporary manifestation of his selves. What revived Banner inside the Hulk was Rick's concern and worry, coming through the mind link, making Banner realise someone still belived in him, slowly urging him to try again. The repeated use of Gamma rays, as a part of, he thought, controlling the transformations (I agree with Peter David: It was in reality his MPD) mutated his flight power out of him. But his wishful thinking conviction that this would allow part of Banner's intellect to remain, forestalled the emergence of the Savage Hulk for a time. While linked to the Hulk, Rick finally reached the point where he could almost speak through the Hulk's mouth (look at the final part of his fight with the Ringmaster). This growing unity may have also scared Rick, making him fear that Banner was gone forever, hence amplifying the emotions coming through the link.
Theory by NeroDart (Thanks for your contribution!)

Now that we know that the Proffessor Hulk is not the merged Banner, but a hypnotically created perfected version of the same... Doc Samson DID try to merge the personalities. But it couldn't hold. There was one thing that he couldn't deal with: Banner is an MPD (Multiple Personality Dissorder). But one with a huge difference: Each personality has a different body, with differing qualities. Each personality experiences LIFE and is a different BEING. In short, the selves JUST DIDN'T BUY IT that they were merged... So soon after, they split apart again. Banner had been in a crisis situation, his prime selves were in the same body arguing with each other. Any longer and Banner might have split into yet more personalities, yet more Hulks. Restoring the Banner Hulk would never have worked. And it might have prevented the events leading to the Pantheon. Betty would know it was Bruce inside the Hulk, and would not have rejected him, and Banner would have gone off with her, rather than to the bar with the Ringmaster and Doc Samson.
Theory by NeroDart (Thanks for your contribution!)

Banner was savagely abused by his father. And verbally abused. The young Banner, partially had to assume there must be something evil in him. Something unimaginably evil. Or why would bad things happen to him? Or to those who cared for him, like his mother? He believed that in him, was a monsterous evil... undefined and dark. The Devil Hulk is that vision. The image of the evil inside him made real. He is a creature of nightmare, and like all creatures of nightmare there is no limit to his evil. Banner the concious self, sees himself as good, so the buried evil must hate him, and all that Banner Loves. Evil hates good QED. His energy was, in the young Banner's mind, his evil. So therefore there is probably no limit to his power, as with the Savage Hulk. The madder he gets, the stronger he gets. But as long as he is trapped in the the soul cave, that cannot work. The presence of the Savage and Grey Hulks limit this. If he gains total control, I think it's possible he may transform now and then, but it will be under HIS control. The Banner he becomes will be the Devil Hulk, hiding behind Banner's face. Like all real evil, hiding and lying comes naturally to him. And besides, as Banner, he'll find it easier to get to a laboratory, and there, free from Banner's morality...
Theory by NeroDart (Thanks for your contribution!)

"Out of the hurt comes strength...INCREDIBLE strength". The Hulk is mighty because he was so feeble when it began, he is titanic because he was so human, his humanity was-is the source of his superhumanity. The subtle minutae of the mind, becomes the stuff of the story, of possible future incarnations and alternate worlds. The Hulk is so primal, that he can fit into any fictional universe, let me repeat... ANY!
Theory by NeroDart (Thanks for your contribution!)