.Hulk Jr. is the son of the
from an alternate reality. He was raised as his own by the Hooded Man (Wolverine from the Old Man Logan storyline).
Hulk Jr. is a brilliant scientist like his father and the protege of Mr. Fantastic. But things were bleak in this reality, Earth was dying and so were it's people. Under the command of the Invisible Woman, Hulk Jr. was able to construct a time machine to send himself and the New Defenders back in time in order to create a better time machine with resources from the past. Then with that energy they could take the remaining six billion suffering people of their planet back to the past as well.
Before they could go back, Galactus came to Earth. Hulk Jr. and the New Defenders attacked and subdued Galactus, though with great loss of life, and brought Galactus back to the past with them to power their time machine.
Once in the past, Hulk Jr. set up his machine and the New Defenders captured the Human Torch and Doctor Doom to help power the machine. The Fantastic Four intervened and reprogrammed the device, sending all the refugees to an artificial planet known as Nu-World. Hulk Jr. and the New Defenders went with them to be the super heroes of that world.
Right after the team changed their name to the Fantastic Force, they were attacked by what Hulk Jr. believed to be his mother. He left with her and found out that she was his mother (only what he didn't know was that she was driven insane by becoming the Harpy and was from an alternate timeline). She was able to imprint on him and make him turn against his teammates.
Wolverine would not fight his son, so Natalie X turned on his berserker rage. They kept each other occupied until Psionics used them to knock each other out. When Hulk Jr. awoke, the team was in battle with the remaining Hysteries, a team created by an insane Gaea.
Scarlet Witch then siphoned the gamma radiation from Hulk Jr. to minimalize the threat he posed. Without his Hulk form, which he was brilliant in, he was far superior mentally. It would seem the gamma was making him dumber than he really was.
With his new found intellect, Rob was able to make a device to transport the Hysteries back to their proper timelines. He then used one of Reed Richards' time devices to go back to their dying Earth (with Wolverine, who Gaea had reduced to a walking skeleton). Back on their original world, Gaea gave Rob his gamma powers back, thus reducing his intelligence. In order to save both worlds, Wolverine stayed behind to help Gaea get her sanity back. He and Rob said their goodbyes and Gaea sent Hulk Jr. back to Nu-World.
Things went wrong though and the sun of Nu-World collapsed into a black hole. This caused time to accelerate and the people to revolt and wage war.
Lightwave and Alex Ultron took control of the world and used Natalie X to control as many of the populace as they could. Although not fully explained, it would seem Hulk Jr. have moral objections to this and he was taken prisoner.
When the Thing and the Human Torch came to Nu-World for a visit, Thing was captured as well. Hulk Jr. was rescued with the Thing where he punched and killed Lightwave's daughter Psionics, who was attacking them. Hulk Jr. remained behind saying he had unfinished business with Lightwave.
Hulk Jr. would eventually become the Maestro.