The tremendous forces released by the accident opened a wormhole between Earth's dimension and the dimension containing the immensely powerful entity later known as the Beyonder. During the following years, the Beyonder observed Earth and its multiverse through the interdimensional pinhole.
The day after the accident, the president of Acme Atomics fired Reece for his carelessness. Angered, the Molecule Man covered the president and his desk with ice that he formed from molecules in the air. Reece became a criminal and was now out to use his powers to take revenge on a world he believed had belittled and persecuted him. Yet Reece was so filled with self-doubt, fear, and self-hatred, that he rendered himself vulnerable by unconsciously imposing limitations on his powers. He believed himself to be able to affect only inorganic molecules (and hence unable to affect living beings with his powers).
Uatu, the alien Watcher whose task it is to observe Earth, recognized the dire threat that the Molecule Man posed to the multiverse. Uatu alerted the team of superhuman champions known as the Fantastic Four of the threat posed by the Molecule Man. The Fantastic Four used Reece's self-imposed inability to affect organic molecules to defeat him, and the Watcher transported the Molecule Man to confinement in an other-dimensional world where time passes at an accelerated rate.
Believing himself unable to escape, Reece created a humanoid construct to serve as his companion, and through unknown means endowed it with consciousness. Reece let the construct believe itself to be his son. Before dying, Reece transferred his consciousness and powers into the wand his son carried. Not bound by human limitations, the construct, known as the new Molecule Man, escaped the world and went to Earth, bringing the wand with him. In an attempt to avenge his father, the new Molecule Man battled both the Man-Thing and the Thing of the Fantastic Four, using Reece's powers through the wand. Dependent on the metal wand to maintain his existence in this dimension, the new Molecule Man disintegrated when the wand was taken from him.
However, the consciousness and powers of the original Molecule Man remained within the wand, and the Molecule Man could overpower the minds of whoever touched the wand and take control of their bodies. He took mental possession of Cynthia McClellan, and through her battled Iron Man. Molecule Man then took mental possession of Aaron Stankey and Mister Fantastic. The wand passed through the hands of a succession of holders until Reece's mind recreated his mutated body and transferred his consciousness and powers out of the wand and into the body. He threatened to destroy the world, but was persuaded by the Avenger named Tigra to give himself up and seek psychiatric help.
Reece did so, and soon began to change. He now had simple goals: true love, friendship, and a good home. However, Reece found himself sent to Battleworld, the planet created by the Beyonder, as part of the small army of criminal super human beings that were to engage in the first Secret War. Impressed by the charismatic criminal leader, Doctor Doom, Reece agreed to help fight the superheroes also brought to Battleworld. During the course of the war, Reece and a superhuman called Volcana fell in love with each other. Doom eventually succeeded in stealing the power of the Beyonder and transferring it into himself, both only temporarily. Believing himself abandoned by Doom, Reece threatened to kill him. But Doom helped Reece break through his mental blocks and realize that his power was greater than he had believed. No longer angry at Doom, Reece used his powers to transport himself, Volcana, and most of the criminals back to Earth. On Earth, Reece and Volcana began living together quietly in a Denver suburb, and Reece took a new job as a worker in an atomic plant.
But then, months later, the Beyonder, again in possession of his full power, came to Earth in humanoid form seeking emotional fulfillment. When he failed, the Beyonder decided to rid himself of the problem by obliterating the multiverse. Reece attempted to save the universe by destroying the Beyonder, but the Beyonder's immense power far surpassed even Reece's own. Ultimately, Reece joined forces with many of Earth's superhuman champions to battle him. But the Molecule Man exhausted himself fighting the Beyonder, who unleashed an immensely powerful blast of energy to destroy Reece and his allies. The blast ripped open Earth's crust in the area of the Rocky Mountains, and would have caused incredible planet-wide instability if not for the Beyonder's power. The Molecule Man used his power to shield himself and his allies, and to remove every living thing from the path of the blast to safety. But as a result of his monumental efforts, Reece had severely injured himself internally.
His foes appearing to have been defeated, the Beyonder proceeded with his new plan to find fulfillment by using a complex machine to transform himself into a mortal being with his full power. The machine drained the Beyonder's power into itself, transformed him into a mortal baby, and then began transferring the energy back into him. The infant would soon again become an adult. The Molecule Man and his allies found the machine, and Reece, believing they could not take the chance that the newly reborn Beyonder would not someday destroy the multiverse, decided to kill him while he was vulnerable. Reece wrecked the machine, causing the infant's death, and diverted the Beyonder's immense power, which the machine released, through an interdimensional portal into the dimension from which the Beyonder had originally come. There the energy created a New Universe.
The injured Molecule Man and the Silver Surfer, uniting their power temporarily, repaired all the damage done to the Earth, restoring the mountains and the part of the crust that the Beyonder had destroyed. Reece, believing that Earth's superhuman champions would always worry about his misusing them, pretended his powers had been burned out. Among his allies, only Volcana and the Silver Surfer know that Reece still has his powers, which have since returned to full strength. Reece lived quietly for a time with Rosenberg in their Denver suburb.
A brief bout of instability resulted in the altering of Mount Rushmore to honor his girlfriend, among other things. Fortunately Reece was able to understand he needed more therapy, though this involved kidnapping of Doc Samson. Samson wasn't happy to be kidnapped but was willing to help.
Reece was briefly merged with the Beyonder, in order to take part in the creation of the being known as Kosmos. He managed to separate himself and return to Earth. He was then defeated in combat by Klaw, and separated from Volcana. Molecule Man was later placed under the mental control of the Puppet Master. Reese was used by him to combat Aron the Rogue Watcher, and was defeated by him. It is unclear if after these events he still possesses his previous level of power.
He was listed as one of the Raft escapees after the events of New Avengers #1.
Although the energies that gave Owen Reece his powers came from the same power source as the Cosmic Cubes, Owen Reece generally does not use this capability to the same extent as "true" Cosmic Cubes do, limiting himself to manipulation of "mere" matter and energy. Regardless he has been able to effortlessly recreate an entire galaxy even in his regular state, and on a later occasion unleashed his 'darkest aspect', which possessed sufficient might to fight, and overpower, the Beyonder in a more than 3-dimensional battle, which in turn was claimed by Kubik to be far less than his full potential.
Originally, the Molecule Man subconsciously imposed mental blocks on himself to prevent his using his powers to their full potential. Hence, he believed his powers were ineffective on organic molecules. Although he overcame this mental block in the past, for unknown reasons he is again unable to control organic molecules. Also the Molecule Man formerly had a psychological dependency on using a steel rod ("wand") to focus his powers but he subsequently learned how to direct his powers without it. While the Living Tribunal has stated that the Molecule Man's power is practically limitless, Reece himself has stated it to be below that of Eternity and the Tribunal. It is unknown how he compares to the Celestials, as Kubik similarly once claimed that these space-gods possess power several orders above its own.