Simon Williams is the son of rich industrialist Sanford Williams, owner of Williams Innovations. Simon inherits the munitions factory after his father's death, but the company's profits fall due to its biggest competitor, Tony Stark. On the advice of his brother Eric, Simon tries to embezzle funds from his company but is caught and incarcerated. Simon blames Stark for this and accepts the proposition of master villain Baron Heinrich Zemo after the Enchantress pays his bail, as a pawn is required to infiltrate the Avengers. The desperate Simon Williams agrees and is transformed into an ion-powered being with superhuman powers. His powers are tested, and he is shown to have great superhuman strength and durability, even defeating the Executioner. Called Wonder Man by Zemo, he is then sent to meet and join the Avengers, with instructions to betray them at a critical moment so that Zemo's Masters of Evil can destroy the Avengers. Zemo ensures Wonder Man's loyalty by advising him that as a result of the treatment his body now requires periodic doses of a serum to survive—a serum that only Zemo can provide.
The Avengers were lured into a trap and captured. The plan fails when Wonder Man decides to save the Avengers and aid them against Zemo, apparently at the cost of his own life. Iron Man (Tony Stark) records Wonder Man's brain patterns in the hope that one day he can be revived. Unbeknown to the Avengers, Wonder Man's body has simply entered a catatonic state as it adjusts to the effects of the treatment. Eric Williams becomes distraught over the apparent death of his sibling and, blaming the Avengers, assumes the identity of the Grim Reaper in an effort to destroy them. The Grim Reaper steals Simon's body at one point, and attacks the Avengers three times before Wonder Man finally returns.
Wonder Man remains in suspended animation for years, and it is during this period that Ultron, the evil robot creation of Henry Pym, steals the brain patterns recorded by the Avengers for use as a template for the synthezoid Vision. It is later revealed that Vision is built from the original Human Torch, an android created by Professor Phineas Horton. This only happened in mainstream continuity and other origins were possible courtesy of the Forever Crystal of Immortus.
During this vulnerable time, Wonder Man is used as a pawn on three occasions. Wonder Man is briefly revived by Kang the Conqueror to battle the Avengers as part of his Legion of the Unliving, and later "resurrected" as a zombie by Black Talon and the Grim Reaper to attack the Avengers once more. On the final occasion, the Living Laser hypnotizes a now-awake but still very weak Wonder Man, in an unsuccessful attack on the Avengers. After this encounter, Wonder Man was restored to true life and chooses to remain with the Avengers, aiding them against Attuma and Doctor Doom. He also fought the Vision, and helped the Avengers battle Graviton. He soon after defeats the Grim Reaper, who was intent on destroying the Vision as he was "artificial" and a "mockery" of his brother; Wonder Man at this point is revealed to have become a being of ionic energy.
Wonder Man eventually joins the Avengers in a full-time capacity and becomes close friends with his teammate, the Beast. For several months after his resurrection, Wonder Man suffers from slight claustrophobia and a fear of dying in battle, as he did once before. Wonder Man finally overcomes his fear of death during the final battle with Korvac. Wonder Man invaded his former plant which had been taken over by the Maggia, and fought Madame Masque and the Dreadnought. Developing an interest in acting, Wonder Man stars in minor roles before moving to Hollywood, where fellow Avenger Hercules uses his contacts to establish Wonder Man's career. Wonder Man also works for a time as a stuntman, an ideal vocation since he is invulnerable to virtually all conventional weapons.
Wonder Man helps form the West Coast Avengers, and his new-found confidence begins to become arrogance. He develops a serious rivalry with Iron Man, but sees the error of his ways after a brutal battle with the Abomination. He also foils Doctor Doom's plot to control the world. Wonder Man eventually accepts the Vision as his "brother," but there is a setback when the Vision is dismantled and rebuilt as an emotionless machine by a global conglomerate. The Scarlet Witch—the Vision's wife—asks Wonder Man to provide his brainwaves once again in order to rebuild the foundational personality matrix of the original Vision, but Wonder Man refuses, having feelings for her himself. The Wasp further deduces that the Vision's original relationship to the Scarlet Witch may even have been predicated by Wonder Man's initial donation for the original personality matrix; at this, Wonder Man confirms that several of his hesitations about making the attempt arise from these doubts and the subconscious desire he's felt toward the Scarlet Witch since her separation from her husband. He is then ensorcelled by the Enchantress, and battles the Avengers.
Wonder Man battles old foes Goliath and the Enchantress, before meeting his would-be sidekick "Spider" and battling Gamma-Burn, resulting in wrecking his jet-pack. Wonder Man then battles the assassin Splice for the first time. Wonder Man takes part in the Kree/Shi'ar War, and had his powers altered when he and the Vision failed to prevent the Shi'ar Nega-Bomb from detonating. He battled Angkor, and then journeyed to Hades where he battled Mephisto, Blackheart, the Enchantress, and the Grim Reaper; he then learned that he was immortal. When Avengers West Coast (renamed) disbands after a dispute, Wonder Man becomes a founding member of its successor group— Force Works. Soon after this, an accident in space changes Wonder Man into a being of pure ionic energy, and during a related mission against the alien Kree, Wonder Man is disintegrated in an explosion. Many months later, the Scarlet Witch accidentally resurrects Wonder Man in ionic form; while in this form he appears when she is in need. Several months later, the Scarlet Witch is able to fully revive Wonder Man and he now exists in an independent, more human form. It is also discovered later that the Grim Reaper - dead at the time - is also revived. Wonder Man becomes romantically involved with the Scarlet Witch, but ends their affair during the Kang Dynasty saga, due to her residual feelings for the Vision.
Wonder Man is blackmailed into working for S.H.I.E.L.D. during the Civil War storyline. Due to charges of misappropriation of funds in his non-profit organization, Wonder Man is pressured to work for the pro-registration side in the ensuing Civil War drama. In addition to capturing renegade vigilantes and criminals, Wonder Man is instrumental in creating televised messages to educate the public and yet-unregistered superhumans about the specifics of the Registration Act. Wonder Man became a member of the Mighty Avengers.
Wonder Man began a romantic relationship with fellow Mighty Avenger Ms. Marvel warning her not to use her position as leader of the Avengers to keep him out of potentially dangerous situations just because of their relationship.
Following the events of the Secret Invasion, Norman Osborn created a new team of Avengers, effectively retiring Wonder Man during the Dark Reign storyline. Wonder Man later appears on television, lamenting his tenure as an Avenger, claiming it was all a waste of time, and that using violence to uphold justice has caused nothing but heartache and death. He ends his speech by sadly admitting that having Osborn in charge is exactly what the country deserves. After this, Wonder Man is imprisoned as a member of the new Lethal Legion. This group opposes the tyrannical efforts of Norman Osborn; Wonder Man joins to try to keep them from hurting innocents.
Wonder Man has been seen alongside his old West Coast Avengers teammates, Ronin, Mockinbird, Tigra and War Machine in battle with a new version of Ultimo.
During the Heroic Age storyline, Simon is approached by Steve Rogers to join the new team of Avengers. Simon refuses stating that the Avengers have caused more problems than they have solved and implies as Rogers leaves that he will make sure his old allies realize the mistake they are making. Simon also mentioned as having been in jail until Steve bailed him out. After learning that Rogers had disregarded his advice, Wonder Man attacks the new team causing some damage to their base before inexplicably disappearing. Thor and Iron Man later contact him to try and reason with him, but Simon refuses to listen to their arguments, stating that the dead heroes that have resulted from the Avengers working together should be a clear sign that the concept is doomed, departing as Thor and Iron Man try to argue that all heroes are aware of the risks when they begin. Significantly, Iron Man notes that Simon is 'leaking' ionic energy, suggesting that his current mental condition may relate to his powers rather than being simply a matter of choice. Wonder Man put together Revengers, a team of super-powered people to stop the Avengers because he believe they do more harm than good, blaming the Avengers for Ultron's existence, the damage caused by the Scarlet Witch and the Hulk, the Civil War, and Osborn's Dark Avengers. His team subsequently defeats the New Avengers in a quick attack on the mansion before he moves on to attack Avengers Tower, stating that he will destroy the tower unless the Avengers immediately disband. Although Iron Man manages to trap him in a prison specifically designed to contain his ionic energy with the Revengers being quickly defeated by the combined Avengers teams, Wonder Man has still successfully managed to spread doubt among the population about the merits of the Avengers as a concept particularly since Captain Rogers has yet to officially rebuff any of his arguments, asking Beast to remember his words simultaneously reflecting that he may be able to see the Avengers from the outside as he has not been 'real' since his resurrection before he apparently disappears from his prison.