Seeking a bride, Ultron kidnapped the Wasp, brainwashing her then-husband and Ultron's creator, Henry Pym (Ant-Man), into transferring her life energies into a newly built robot: Jocasta. Jocasta acquired the Wasp's personality, emotions, conscience, and ability to control insects, but not her memory. Realizing that the Wasp must die for her to live, Jocasta used that cybernetic insect control to summon the Avengers, who stopped Ultron and reversed the transference, saving Jan but shutting down Jocasta. Unknown to the Avengers, Jocasta still retained some portion of the Wasp's essence, but she remained inert until activated from afar by Ultron. Battling free of the Avengers, Jocasta returned to Ultron's side but quickly realized he was irrevocably evil and aided the Avengers against him. After Ultron's defeat, Jocasta and several Avengers were kidnapped by the Collector; the remaining Avengers soon freed Jocasta and the others, learning of the oncoming universal threat of Korvac in the process. Jocasta aided the Avengers against Korvac, her cybernetic senses detecting vital clues that helped to locate him. When the government soon forced the Avengers to contract to only seven members, Jocasta remained with the team, self-deprecatingly identifying herself as a "mere machine" and thus not subject to the group's size limits.
Jocasta attempted to bond with individual Avengers, but continually felt shut out. Even the android Vision, who was having emotional problems of his own, repeatedly ignored Jocasta. Having nowhere else to go, she remained with the team and aided them against Django Maximoff and the Taskmaster; after defeating the Taskmaster, Captain America and Iron Man offered to make her a full Avenger at the next business meeting. However, Jocasta remained a probationary member while aiding the team against Red Ronin and assisting in Ms. Marvel's delivery of the child Marcus. When Ultron next threatened the Avengers, he recognized Jocasta as a prime threat and mind-controlled Iron Man into disabling her, but she restored herself with the aid of Edwin Jarvis and continued to aid the team against the Yellow Claw, Pyron, the Leader, the Shadow Lord and the Berserker, and the Brotherhood of Evil Mutants.
Jocasta never received her promised status as a full Avenger, and only learned from Jarvis of an emergency meeting called about the threat of the Weathermen. After Jocasta single-handedly faced the power behind the Weathermen, the rogue sentient weather station Samarobryn, the Avengers held a meeting to determine their new membership that same afternoon, and again Jocasta was apparently forgotten. Jocasta wordlessly left the team (who had intended to offer her a lesser "substitute" status with them). Her metallic skin preventing her from fitting into society, Jocasta was rejected by humanity and retreated from all contact with people until her cybernetic senses began to malfunction. The Fantastic Four discovered the cause of the malfunction was an attempt by Ultron to resurrect himself, and the Thing and Machine Man came to Jocasta's aid. Though Machine Man and Jocasta began to bond as close friends, ultimately Jocasta sacrificed herself in a futile attempt to destroy Ultron.
Seeking inside information about the Avengers, the High Evolutionary recovered Jocasta's parts and reconstructed her. She sent an emergency signal to the Avengers, who came to her aid. Again, Jocasta sacrificed her body to destroy the foe, this time preventing the detonation of a genetic bomb which would have altered mankind. However, Jocasta's head survived the explosion, and her memories and personality remained intact, though dormant. The head was recovered by the Avengers who, unable to do anything with it, transferred her to the keeping of her friend, Machine Man. Working on restoring her, he was interrupted by one of the metal-devouring Termini and fled with Jocasta's head. Both Machine Man and Jocasta were taken to a nearby factory belonging to Sunset Bain (Madam Menace), where Bain covertly duplicated Jocasta's head and returned a sabotaged copy to Machine Man. The head was later stolen by Mechadoom and re-retrieved by Machine Man, who, unaware of Bain's interference, was unable to resurrect Jocasta.
Ultron eventually attempted to create another bride, this one titled Alkhema (War Toy) and created from the mind of the Avenger Mockingbird, but without conscience. This bride also rebelled against Ultron, and subsequently created her own robotic society beneath Egypt. When Ultron revealed that he'd pre-programmed the creation of this society into Alkhema as a means to recreate himself, she and her robotic civilization fought back. While Alkhema and the society were apparently destroyed, one lone bio-synthezoid survived, calling itself Antigone. As an unfinished and uncontrolled child, Antigone left of its own free will with Ultron.
Sunset Bain, meanwhile, made only limited progress with Jocasta until she hired Tony Stark (Iron Man) to decode the artificial intelligence program. The unique multidimensional operating system let Stark recognize the A.I. as Jocasta, and though Bain had a degree of control over her, Stark and Jocasta were able to free her from Bain's control. Once again, Jocasta self-destructed, but this time not before transmitting herself into Iron Man's armor, from which she was downloaded into a Stark super-computer. Having been unhappy in a mechanical body, Jocasta was content to remain as a disembodied A.I., and aided Tony Stark with the running of his business, research, and households as well as aiding Stark, in his Iron Man identity, with information on and analysis of his foes, all while pursuing the study of several advanced fields at electronic speeds. When Tony Stark was infected with an aggressive nanovirus created by Justin Hammer, Jocasta took a more active role, aiding James Rhodes in restoring Stark and then aiding them against Hammer.
Shortly thereafter, Stark's Iron Man armor gained sentience and "attacked" Jocasta electronically, repeatedly violating her and traumatizing her, though she kept this a secret until the sentient armor returned, this time revealing itself to have been a crude form of Ultron. Jocasta overcame her fears, fighting Ultron electronically while Iron Man did so physically. The two destroyed Ultron yet again, accidentally deactivating Antigone in the process, and in the resulting explosion Jocasta sought refuge in the only place available: Antigone. In her new form she was seen leaving with Ultron's presumably now-empty head in her arms. Later, inexplicably back in her classic form, she opposed the maddened Scarlet Witch alongside the Avengers.
An alternate Earth's Jocasta also exists on Earth-616, one of the extra-dimensional Gatherers summoned by Proctor to oppose the Avengers. She had a more military appearance than Earth-616's Jocasta did, and was golden instead of silver, but otherwise both seemed to have very similar powers. She was subjected to programming erasures by the Gatherers' "Anti-Vision," which left her with the personality of a 1940s detective novel dame after the Anti-Vision's destruction. The Vision attempted to help Jocasta adapt, but returned to the Avengers without giving an explanation of Jocasta's status.
In one alternate future (Earth-8410), Jocasta remained in Sunset Bain's service for over 40 years. She eventually reunited with Machine Man but, despite her affections for him, decided to remain with Bain through the remainder of Sunset's life. In another future, Jocasta, in Antigone's body, married Machine Man and bore his child while fighting alongside Killraven against invading Martians.