Parasite is a Superman villain capable of draining the energy of his victims. A number of versions of the character exist, the most prominent of which has been Rudy Jones.
Raymond Maxwell Jensen was a lowlife who got a job as a plant worker for a research center. Wrongly believing that the company payrolls were hidden in storage containers, Jensen opened one and was bombarded with energies from biohazard materials (which was actually waste collected by Superman when he traveled into outer space), which transformed him into a purple skinned, parasitic entity, becoming the Parasite; any time he touched someone, he could absorb their physical and mental properties. Touching Superman would instantly absorb a sizable fraction of his superhuman powers (it was established early on that he is not capable of acquiring the whole of his powers). On one occasion, while attempting to absorb a greater portion of his adversary's powers than previously, his body disintegrated for a period of time due to the pressure to his cells. Despite these abilities, the Parasite became depressed because he could no longer embrace his wife and children. The Parasite made a number of reappearances before the Crisis, yet he never successfully found a means to permanently defeat Superman. Despite this, he had knowledge of his foe's alter ego and often used this to attack Clark Kent. Gaining sizable intellect from his multiple encounters with Superman, Parasite devised the means to reanimate dormant plant remains left behind from the Earth-Two supervillain Solomon Grundy, creating a newer and stronger version of the creature to plague his adversary. On another occasion, Parasite devised the means to transfer the powers of the hero Air Wave to the young hero's adversary Davy Jones temporarily.
Parasite was one of the main characters in the second Marvel/DC crossover between Spider-Man and Superman (Marvel Treasury Edition #28). In this story, he was recruited by Doctor Doom as an agent in Doom's latest plan to conquer the world by wiping out all power sources but his own fusion reactor. Doom claimed that he needed the Parasite to function as an invincible bodyguard, capturing the Incredible Hulk and Wonder Woman and giving the Parasite a harness that would allow him to retain their powers for prolonged periods. However, Doom's true intention was to kill the Parasite by allowing him to absorb so much power that his cells would burst, causing Parasite to- according to Doom's calculations- transform into a crystalline mass that would allow Doom to perfect the reactor by using its energy-manipulation abilities to control the reactor's power output. This plan was thwarted when the Parasite briefly absorbed Spider-Man's powers, causing his borrowed spider-sense to alert him to Doom's treachery and turn on Doom, although he was subsequently defeated by Superman using a gauntlet of Doom's that prevented the Parasite from absorbing his energy when he was attacked.
Originally a menial slacker, Rudy Jones was transformed into the Parasite while working as a janitor at a Pittsburgh S.T.A.R. Labs facility. Unknown to anyone at the scene, the Lord of Apokolips, Darkseid, remembered the Pre-Crisis Parasite and manipulated Jones to become the modern version. He made Rudy think that a waste container might have held something valuable. He opened it and was exposed to strange radiation that changed his body into the bald, green-skinned villain (Parasite 1.0). Jones now had the ability to absorb the life energy of other people, leaving smoldering skeletons. This power was necessary for his survival as his own body is in a constant state of hunger for energy that it can't sustain on its own. During this time, Martin Stein, one half of the Firestorm matrix (Ronnie Raymond being the other half) learned he was dying and decided to destroy all the nuclear weapons in the world. This did not sit well with Earth's governments, particularly the United States, who sent the Suicide Squad to Times Square, where Firestorm was holding a press conference. Things quickly got out of control as the Squad and the Justice League, both intent on subduing Firestorm, fought one another, and the Parasite (who was brought on the mission against the protestations of both Amanda Waller and Colonel Rick Flag Jr.) is released. He goes on a rampage and apparently kills Multiplex, only being brought under control by the cooperation of both teams. Later, he attacked the new Firestorm, who easily subdued him and left him near death.
During one of his stints at Belle Reve Prison, doctors attempted to make him human again. Despite their intentions, the doctors only managed to change his skin color to the more familiar purple and also inadvertently increased his absorption power, enabling him to feed on other forms of energy, such as electricity and heat (Parasite 1.5). After a number of years, the Parasite became involved in the plot to save Superman from overloading on solar energy. Rudy and Superman battled on the moon where Superman uncontrollably unleashed an immense blast of heat vision that the Parasite absorbed, causing him to mutate even further into a huge, hulking monster with teeth resembling a leech's. This mutation (Parasite 2.0) again increased Rudy's draining abilities, allowing him to absorb fast-moving objects' inertia, as well as making him impervious to telepathic attack to an unknown extent, since he could now drain energy through a mental link as he displayed when Dubbilex telepathically attacked him. His extra size and power did have a downside, however; he needed to absorb more energy more frequently in order to stay alive.
Unfortunately for a scientist that was tending to Rudy during one of his terms in imprisonment, he was tricked by Lex Luthor and somehow absorbed into the Parasite. This joining was different from Rudy's others as, apparently due to unspecified modifications to Rudy's physiology during this stint at S.T.A.R. Labs- although some sources speculate that the scientist's strength of character contributed to his 'survival'-, he actually retained the scientist, Dr. Torval Freeman, as a part of his own mind. This combined intelligence made the Parasite even more menacing, given Freeman's superior intellect. He is later recruited by Morgan Edge to be part of the second Superman Revenge Squad. After Superman's powers were converted into energy-based ones, the Parasite returned to see what he could absorb from the Man of Steel. However, at this point in time, Superman was not in full control of what was happening with his powers and nearly killed the Parasite. Later, Parasite returned once again, looking to make trouble for Superman, but finding himself facing off against Supergirl instead, absorbing some of her new angelic powers and nearly killing himself due to the 'divine judgment' of Supergirl's new 'wings'.
At one point, Rudy was contracted to help drain off a being named Strange Visitor's excess electromagnetic energy as she could not fully control it. This exposure to Strange Visitor's power caused the Parasite to mutate again, giving him the ability to fully and permanently retain the intellects of all of his victims and also allowed him to maintain any stolen energy for up to twenty-four hours. Like Torval Freeman, Rudy also absorbed an unknown shapeshifter into his biology, granting him the permanent power to mimic the exact genetic makeup and appearance of his victims (Parasite 2.5).
After he later escaped from S.T.A.R. Labs in the early 2000s, the Parasite began to form a plan to get back at Superman. He began stalking Lois Lane and Jimmy Olsen in an attempt to get to those closest to Superman. The Parasite had taken the form of one of his previous victims, an old man, and was run down in the pandemonium that evening when Lois came to his aide. Not realizing that she was actually in contact with the Parasite, a simple touch was all Rudy needed to get her knowledge of Superman. Rudy was surprised to learn from Lois Superman's secret identity. A new plan formed when he realized how close Superman actually was to Lois; the Parasite decided to take her place and tear him down emotionally by pretending to be a scorned Lois Lane, apparently even having an affair with Luthor in the process. When Clark attempted to confront Lois about her recent distance from him, in a fit of rage uncharacteristic of Lois Lane, Rudy punched Clark out of their apartment and into the streets of Metropolis. Shortly after this display, Superman got the Parasite to reveal himself in the guise of Lois Lane. Rudy couldn't handle the fact that anyone other than himself as the Parasite took down the Man of Steel. Just as the Parasite was about to lay the final blow to an exhausted Superman, Rudy drops, completely crippled by kryptonite poisoning he had drained from Superman, unbeknownst to either Rudy or Clark. Superman finally realized the reason he has felt so weak recently was because he was being constantly drained by the Parasite and also the victim of the mysterious kryptonite poisoning. When he asked Rudy how long he had pretended to be Lois, the Parasite related his story to the Man of Steel. In his final moments, he tells Superman that he still needed to have contact with Lois once every twenty-four hours to maintain his charade, confirming that she is still alive. He also told him that Lois loves him more deeply than he could ever know, and loves him in a way that nobody ever loved the Parasite. The Parasite died before he could tell Superman where Lois was imprisoned (Superman [vol. 2] #157). Although Superman initially tried to investigate himself, his efforts were hampered by a bout of kryptonite poisoning, and Steel was forced to contact Batman to help the investigation. Accompanied by Superman, Batman tracked a spree of recent disappearances to the Parasite's hiding place- during which Superman gained a new insight into Batman's methods and actions-, and Lois was soon found alive by the two heroes. Lex Luthor, with whom it is implied the Parasite had engaged in amorous, "extramarital" activity while in Lois' form, was infuriated when he learned of the Parasite's schemes. As such, Luthor went to great efforts to obtain the Parasite's remains.
In Justice League of America (vol. 2) #2, the Parasite is found to be holed up in St. Roch, Louisiana, where he uses his power-absorbing abilities to temporarily neutralize the powers of villains, for a fee, so they might evade detection during the course of criminal efforts. It is not explained how Rudy survived his apparent death by kryptonite poisoning several years earlier, although Jones has shown in the past to be capable of regenerating his entire body from being burnt down to the skeleton, so he may very well have simply healed from the kryptonite radiation. How he escaped Lex Luthor's custody is another question entirely. There is also the possibility that this Parasite may not even be Rudy/Torval at all; his face is lacking the monstrous teeth that the Parasite has had for most of his career, his vocabulary is more sophisticated than what is normally associated with Rudy Jones, although this may be a result of Torval Freeman possibly being the dominant personality currently, and his costume is the one worn by Maxwell Jensen, which the Post-Crisis Parasite had never worn before. The only characteristic of the Parasite shown in Justice League of America that is consistent with previous appearances of Rudy Jones would be his hulking physique. On a side note, he also recognized Black Lightning.
In Action Comics Annual #10, a headshot of the Parasite was seen as part of "Superman's Top 10 Most Wanted" that bore a resemblance to the version seen in Justice. This version of the Parasite later appeared in Action Comics #751 wearing the Superman: The Animated Series-inspired costume Parasite wore circa 2000, and is later seen as a member of the new Injustice League. It has not yet been revealed if this Parasite is the same that appeared in Justice League of America (vol. 2) #2, but he has been revealed to be a resurrected Rudy Jones by Lex Luthor in Superman: Last Son.
He can seen as the member of Libra's Secret Society of Super Villains.
In the New Krypton storyline where 100,000 Kryptionian refugees are freed from the bottle city of Kandor; the Kandorians decide to take it upon themselves to eliminate Superman's enemies. A group of Kandorians break the Parasite out of prison, killing several prison guards in the process and imprison the Parasite in the Phantom Zone. Superman freed Parasite, so he could be taken to Belle Reve, but Parasite escaped.
The 2009-10 miniseries Superman: Secret Origin redefines Parasite's origin. In this version, Rudy Jones is a janitor of the Daily Planet. One day Lex Luthor, as part of a daily "LexCorp Lottery", in which he selects one person from the crowd formed outside the LexCorp building to provide them with a new life, chooses Rudy. Inside LexCorp, Rudy eats a donut which had been accidentally spilled with a purple toxic material (revealed in Issue 5 to have been produced by extracting the radiation from Kryptonite). This transforms him into the Parasite, subsequently going on a rampage in Metropolis until he is stopped by Superman. He was last seen in Issue 5 to be in a holding cell in LexCorp tower, been seen by both Lex and Lois Lane's father, General Sam Lane.