Silver Age (1963-1968)
Larry Trainor was a fearless US Air Force test pilot, much like his friend Hal Jordan, before his life took a sudden and tragic turn. While piloting an experimental plane designated the XP, he found himself accidentally exposed to a radioactive field in the atmosphere while flying in high altitudes. Barely surviving the experience, Trainor now found himself to be totally radioactive, but also exhibiting a bizarre superpower, as he could now release a negatively charged energy being from within his own body.
This negative energy entity was pitch black with bright glow, could fly at high speeds, cause objects to explode, and pass through solid objects unscathed. This being could only exist independently of Trainor for one minute at a time however, and while the negative energy being roamed free, Trainor's physical body would become inert and is totally defenseless. Trainor is forced to wear specially treated bandages over his entire body to protect innocent bystanders from his radioactivity, which could be lethal to them.
After his accident, Trainor was approached by Dr. Niles Caulder, a scientific genius who went by the name "the Chief." Although Trainor was now a freak and an outcast, the Chief offered him a chance to become a hero in his new team the Doom Patrol as Negative Man, a reference to the negative energy being inside of him. Negative Man found a new family with the Patrol, and even fell in love with his teammate Elasti-Girl, although she only saw him as a good friend. After many adventures together, the Doom Patrol seemingly sacrificed their lives to save a small fishing village, and Negative Man appeared to die alongside his teammates in a massive explosion.
Post Crisis (1986-2011)
After his apparent death, the Negative Energy being within Trainor found a new host body, that of Russian cosmonaut, Colonel Valentina Vostok. The being bonded with her, forcing her to become covered in bandages to protect others from her radioactivity just like Trainor once did. Now calling herself Negative Woman, Vostok became a part of the second incarnation of the Doom Patrol. After some time, it was revealed that Trainor's actual mind and soul were within the negative energy being, and only his human body had been destroyed. The Chief, who had also survived the original explosion that had seemingly killed the Doom Patrol, cloned Larry a new body identical to his old one, and the negative energy being left Vostok and returned to Trainor. Vostok eventually died.
Now a member of the Doom Patrol again after many years, his return was short lived, as several team members died during an alien invasion, and the group breaks up. Larry, now hospitalized, learns that the negative spirit also contained its own separate consciousness aside from his, and was capable of independent thought and movement. The negative energy being would trick Larry into fusing him with his doctor, a woman named Eleanor Poole. This new intersexed being now referred to itself as Rebis. Staying with the Doom Patrol for some time, Rebis contains memories of all three individuals, and often uses the pronoun "we" when referring to itself. Rebis is also more powerful than Trainor or Vostok ever were, as it can fly, exhibits psychic abilities, and is seemingly immortal.
At one point, the schemes of the other-dimensional being known as Superboy Prime altered the history of the universe, allowing all the original members of the Doom Patrol to be reintroduced into the DC Universe, with all their past history seemingly erased. This meant that Larry Trainor was no longer a part of Rebis, and was a version of Negative Man that was far closer to his original incarnation.
When the events knows as the INFINITE CRISIS happened, Superboy-Prime broke the Phantom Zone barrier in a pitch battle with several heroes. When that happened, all of the members of the Doom Patrol were able to remember their previous lives that had been wiped from the timeline, an occurrence that was especially traumatic to Negative Man, who had been so many different people over the years.
Post INFINITE CRISIS (2006-2011)
After the Multiverse was reborn due to the events of the Infinite Crisis, Negative Man was once again a member of the Doom Patrol. During this incarnation of the team it is revealed that the negative energy being uses up the bodies that it inhabits after a period of time, and that when one of Larry's host body's expires, the being (which contains the true essence of Larry Trainor) then inhabits a brain dead donor body. Because of this ongoing process, Negative Man obtains the memories and experiences of every host body he's been in, and the entire process can almost drive him insane, so he has to constantly remind himself that regardless of the body he's in, he is in fact still Larry Trainor.
Eventually, the Doom Patrol find a new home base on the remote Oolong Island. Here, Trainor learns to take greater control of the negative energy being, which allows him to use his powers without the one minute time limit. During the events of the Blackest Night, Negative Man fought the Black Lantern version of former Negative Woman, Valentina Vostok. When their Negative entities met, it temporarily created a new entity, which destroyed the Black Lantern ring. Negative Man's friend and teammate Robotman mentioned that this new entity was similar to his time as Rebis.
New 52 (2011-2016)
In the wake of the FLASHPOINT event, the DC Universe timeline was once again heavily altered. In this new history of the universe, the Doom Patrol was once again introduced to the world with the original team line-up, including Larry Trainor as Negative Man. All of their previous history was seemingly erased, including Trainor's
death and his time as the being called Rebis.
This version of Negative Man first appeared when the Doom Patrol went on a mission to capture the powerful Ring of Volthoom, which put them into conflict with the members of the Justice League. It was during this mission that it was revealed that Larry Trainor's original accident which gave him his powers and, as well as all of the accidents of her fellow Doom Patrol members, were all caused by Dr. Niles Caulder in the first place.