Horace Littleton was a scientist for the Weapon Plus program in the 60's, and eventually developed a LSD/Super Soldier Serum hybrid. However, Littleton's project had lost funding as well as test subjects (implied to be somewhat caused by Littleton's consistent recreational use of substances in a reckless manner) so, Littleton injected the serum into himself, which gave him psychoactive powers and the strength of a Super Soldier. After trying to bring down S.H.I.E.L.D, he was arrested and imprisoned for 50 years, with the Iron Nail failing to free him in 1969 thanks to the efforts of the Winter Soldier.
Littleton was eventually broken out of prison by the Iron Nail in the present day, who had befriended him while he was working in S.H.I.E.L.D. Due to the effects of the Super Soldier Serum, he had not aged a day since his capture. He used his bubbles to give Nuke, who was dying of critical wounds, a peaceful and quiet death.
Littleton used his bubbles to control both Maria Hill and Nick Fury Jr , using their credentials to access the top secret Gungnir project, which was a experimental mech that also functioned as a Helicarrier as well. Both him and the Iron Nail planned to use this weapon to start a international war and expose S.H.I.E.L.D. When Captain America attempted to bring down the pair, Littleton was able to overpower him with one of his bubbles, knocking him out and allowing the pair to use him as a pilot for the robot. Steve's illusion tried to convince him that they were defeated, and that he had been safely taken to a hospital while his allies stopped Gungnir, with a massive parade going on for him as well as revealing that Sharon Carter, thought dead by him for a long time, was alive and well.
Steve was eventually able to find out that this was just a illusion, and killed himself in the dream state to escape it. Littleton tried to subdue Steve again, but he was able to use his shield to smash the pipe connected to his head, sending all of his bubbles back into his own head and driving him crazy, to the point of throwing himself off the Gungnir Helicarrier. Through his body was never found, he is presumed to be dead.
Powers and Abilities
Dr. Mindbubble gets his power from a bowler hat he wears which has a pipe that comes out the front. The pipe creates large bubbles which, when encapsulating the head of a person, causes them to enter a mind-altering state. It has been shown that the only way for a subject to escape the consciousness-altering mind bubble and pop it altogether, is to kill yourself in the dream state. His bubbles were also shown to be bullet-proof and strong enough to carry Littleton around.
As well as this, he also has the standard strength and slowed aging that regular users of the Super Soldier Serum also have.