Banner's molecular structure was transformed by the gamma radiation of a bomb when he raced out onto a testing site and saved the life of one Rick Jones.
You're fighting against the inevitable, Hulk. I'm simply the final product of natural selection. The strong survive. I'm the strongest. Isurvived.
--Maestro
The Maestro was a version of the Hulk from an alternate future timeline, approximately a hundred years into the future, combining Banner's intelligence with the Hulk's more malevolent aspects. After a nuclear war killed almost all of the Earth's superhumans and brought the world to the brink of extinction, the Maestro seized control and became the ruler of Dystopia.
Grey haired and balding, the Maestro was clearly older than the Hulk, but was also significantly stronger due to the radiation he absorbed since the war. He ruled the city of Dystopia, built to his own designs and protected by radiation shielding. Brutal soldiers with hi-tech equipment kept the "peace" and imposed the Maestro's iron will. The Maestro himself dwelt in a grand palace, where a bacchanalian atmosphere reigned. Other gamma-irradiated beings, She-Hulk (now calling herself "Shulk") and the Abomination, survived the war and seemed to have conquered other areas of the world.
Not long after the war, an elderly Rick Jones encountered the reality-hopping mutant Proteus, who had possessed the body of an alternate reality Hulk from the year 2099. Proteus intended to discard his current body and possess the Maestro. Jones, unaware of his plan, provided a weapon created by the X-Man Forge, which might have been able to kill Maestro. However, the plan failed when the Maestro was warned by the Exiles, who were pursuing Proteus. Proteus possessed a new host and fled to another world, breaking the Maestro's neck during his escape.
Years later, the Maestro, fully recovered from his injury, encountered a time-traveling Genis-Vell and Spider-Man 2099. Manipulated by the supervillain Thanatos, the three battled, but Captain Marvel and Spider-Man eventually returned to their own time, with no consequence for the Maestro.
Acquiring Doctor Doom's time machine, the rebels opposing the Maestro (led by Rick Jones) eventually decided to bring the "Professor" Hulk forward from the past, hoping that he can defeat the Maestro. The Hulk agreed to help them and confronted the Maestro,[2] but lost due to the Maestro's greater experience, power, willingness to endanger bystanders, and his ability to predict the Hulk's moves in combat. The Maestro broke Hulk's neck to immobilize him, then tried to persuade the incapacitated Hulk that he should side with his future self, telling him that nothing would change when he returned home and he would still be persecuted.
After the Hulk's recovery, the two clashed once more, but despite the Hulk's best efforts, the Maestro was still far too powerful for him. At the last minute, the Maestro was defeated by the use of Doom's time machine, and sent back to the time and place that the Hulk was created: ground zero during the testing of the atomic Gamma Bomb, the only bomb that the Hulk knew the ground zero location of. Appearing next to the bomb itself, Maestro was seemingly killed in the same moment that created the Hulk,[3] but some part of his consciousness still remained, tied to the skeletal fragments at the Gamma Bomb site.
Eventually the Hulk learned that the "homing sense" which had always allowed him to locate ground zero, his "birth" place, was actually attracted to the Maestro's spirit and remains. The Maestro had also been absorbing gamma radiation from the Hulk each time he returned to the site, gradually restoring himself. When the Hulk returned from Counter Earth[4], he was radiating vast amounts of energy. Maestro finally absorbed enough radiation to restore himself to life, although in a weakened and emaciated form.
Shortly thereafter, the Maestro's body gradually rebuilt itself, but he nonetheless fainted from exhaustion, and was captured by Asgardian trolls, who placed his soul into the Destroyer to empower it. As the Destroyer, he battled the Hulk, but as the Hulk and Maestro shared the same DNA, Hulk's spirit was able to enter the Destroyer and defeat it by slamming its visor shut just as it discharged a disintegration beam. The resulting shockwave sent both the Destroyer, and the rock it had been standing on, plummeting towards the Maestro, just shown as almost fully recovered, and the latter was covered by the rockslide.
The Hulk briefly titled himself with this alias during a time when Shrapnel were lodged within his brain.
It was later revealed that prior to the Hulk's arrival Maestro had impregnated a woman, who traveled into the past to raise her son away from his father's influence. Maestro's cousin Shulk traveled into the past along with Kaspin to kill the child and end the Maestro's line, this plan failed when Kaspin killed Shulk with his mental powers.
Creator Peter David has stated on his various message boards that the Maestro was intended to be simply an insane evil alternate version of his Merged Hulk and not a separate personality within Banner.
Real Name
You're fighting against the inevitable, Hulk. I'm simply the final product of natural selection. The strong survive. I'm the strongest. Isurvived. 
