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On the planet Exxor, Fonab and Rua gave birth to twin children, Zan and his sister Jayna. Due to a recessive hereditary trait in Exxorian biology, both twins were born with the mutant ability to alter their physical form. Even as infants, Jayna demonstrated her power to transform into any known Exxorian animal.
While they were still children, a great plague swept across Exxor killing hundreds of innocent civilians including Fonab and Rua. The orphans Zan and Jayna were taken to a special center, but the administrators knew that no surviving Exxorian family would adopt mutant children. Instead, they released the twins into the care of a carnival owner named Dentwil. Dentwil placed the children on display and amused customers with Jayna's ability to transform into Exxorian animals, and Zan's power to turn into waterspouts. By Exxorian law, the twins were the legal property of Dentwil, and could not leave his care until they were twenty years old.
As they grew older, the twins became friends with a sideshow laugh-maker named Illik. Illik grew enamored with Zan and Jayna and elected to raise them as a surrogate father. He also introduced them to his carnival star attraction – the elastic-monk known as Gleek. Although Illik cared for them a great deal, he also recognized that the circus was the only suitable way of life for a mutant. Zan and Jayna wanted more, however.
As Zan and Jayna grew into adolescence, they grew disenfranchised over the fact that they received nothing from Dentwil aside from food and shelter. They approached the circus owner and demanded payment for their services, but Dentwil refused – citing that he owed no legal obligation to them, as they were his private property. Finally, the twins had had enough and they used their shape-changing powers to force Dentwil into relinquishing his hold over them.
Shortly thereafter, Zan and Jayna stole one of the many starships that the carnival used for their interplanetary circuit. Taking Gleek the elastic-monk along as a companion, they rocketed free of Exxor leaving the carnival behind them forever. 
Along their journey, these self-styled Wonder Twins discovered that an alien conqueror known as Grax had intended on taking control of the planet Earth by way of twelve carefully hidden bombs. They piloted their ship to Earth where they met a team of heroes known as the Super Friends. Speaking in Interlac, the Wonder Twins warned Superman of Grax's plans. The Super Friends agreed to provide sanctuary to the Wonder Twins inside of their Hall of Justice, while they individually hunted down the twelve hidden explosives. 
During their stay, Zan and Jayna befriended super-hero trainees, Wendy Harris and Marvin White. Wendy and Marvin became close friends with Zan and Jayna and helped them to adjust to Earth's languages and customs. Wendy and Marvin had plans to go to college and knew that the Wonder Twins would make for an adequate replacement in the Super Friends roster.
After engaging in several adventures with the Wonder Twins, the Super Friends arranged for Zan and Jayna to live with an old scientist friend of Bruce Wayne's named Professor Carter Nichols.  Nichols provided them with a cover identity as foreign exchange students to account for their lack of knowledge of Earth's customs. Supposedly hailing from Eksjö, Sweden, Zan took the name John "Johann" Fleming, while Jayna adopted the identity of Joanna "Johanna" Fleming. Furthering their disguises, Zan began wearing a blonde-colored wig to cover his pointed ears, while Jayna merely used her super-powers to alter her physical shape. With their new Earth identities firmly in place, Zan and Jayna began a new life for themselves at Gotham City High School, but they were always available to aid the Super Friends in times of need.
- Animal Mimicry: Jayna possesses the ability to shape-shift her body into any known animal form. The choice of form is not exclusive to Earth animals but may also include animals from her home world of Exxor, even mythological animals, such as a winged horse. So long as Jayna can envision a specific animal in her mind's eye and is able to correctly name it, she can transform into it.
- Power Limitation: Jayna's super-powers are contingent upon physical contact with her brother, Zan. Direct flesh-to-flesh contact is required to prompt the transformation. Traditionally, this is achieved by one twin knocking their clenched fist against the opposing fist of the other. On one occasion, though, Gleek served as a bridge to allow Jayne to have contact with her brother to activate her powers.
- The character of Jayna was originally developed for the Saturday morning Hanna-Barbera animated series, the Super Friends. Jayna was also featured in the Super Friends comic book adaptation. In 1995, DC Comics writer Ivan Velez, Jr. re-introduced the Wonder Twins as special guest stars in the Justice League spin-off title Extreme Justice.
- Jayna was originally voiced by Liberty Williams. When the series became known as Super Friends: The Legendary Super Powers Show, Williams was replaced with B.J. Ward.
- Jayna's origin was revealed in Super Friends #14.
- Although Jayna's eyes are purple, they were often colored blue in the Super Friends comic book.
- 30 Appearances of Jayna (Super Friends)
- 3 Images featuring Jayna (Super Friends)
- 1 Quotations by or about Jayna (Super Friends)
- Character Gallery: Jayna (Super Friends)