It is said that you shouldn't meet your heroes. Gehaldirah, a high elf of royal bloodline didn't have to meet the realm lord of High Heaven before he became disillusioned.
His admiration for the paragon of the high elf race turned into hatred when he got some damning knowledge about why demons kept attacking his home and looting the sacred tree of life. His hatred for the realm lord turned to self-hatred for his weakness and mediocrity.
Gehaldirah had a moment of introspection. He isn't at the bottom of the ladder in this strength-based hierarchy. He is a king of law, but that apparently isn't enough to guarantee your fate. His strength is also mediocre because it was granted to him because of his bloodline.
He determined he had to change himself. He has to become better. He concocted a plan that is one part genius and one part greed. His plan for reincarnation led him to the trial of heaven that occurs every origin cycle. He needed Origin essence so he participated in the trial.
He got more than he wanted from the trial. His plan for reincarnation would be a success after some adjustments. But now he has a different aim. He won't aim for just the realm lord. The realm lord has control of the High Heaven Realm. That isn't enough for Geraldirah anymore.
He became greedier. He has his sight set on the movers and shakers of the Void Universe. Only the power to subvert the will of World Gods will do. The plan to create LEGION, the ultimate organism was then hatched. If one person cannot achieve something, what about a multitude of them?
His journey will not be easy. He will have to overcome Celestials and their Celestial Supreme, Gods and their GodKings, Demon kings and their Demon gods. The Void Universe is full of obstacles that will like nothing more than to put an end to his path. It is not that they hate him. They will oppose him simply because the era of conquest is coming. There are no friends in the era of conquest. It is everyone for themselves. And he will use everything and everyone for the advancement of Legion.