The Wonder Twins first appeared on The All-New Super Friends Hour on television in 1977 and also made their comic debut that same year in Super Friends #7. While the Super Friends were away, Wendy and Marvin noticed a spaceship had landed on Earth. Hopping on their bicycles, they discovered two humanoid aliens, Zan and Jayna (and an alien monkey named Gleek) dressed in purple. The two arrived on Earth to warn them that the world was in danger. A villain known as Grax had a secret lair on their home planet Exxor. They had overheard Grax's plans to destroy Superman's adopted homeworld. The Super Friends and Justice League were both called in.
The two showed that by joining their hands and commanding their powers to "activate," they could change. Jayna took on the shape of a creature of Exor while took the shape of a wave. After the two were nearly defeated by Grax and were saved by Wendy and Marvin, they announced they were orphans back on Exor and wanted to learn from the Super Friends, just as Wendy and Marvin did.
Finally in The Super Friends #14, their origin was told. On their planet, two races existed, the normal humans and the shape-shifters. Over time the two races inter-married and the shapeshifters seemed to vanish. Once in a while children were born with shape-shifting powers. Unfortunately shortly after Zan and Jayna's birth, a plague hit Exor and the their parents were among the many that died.
Having no other living relatives, the two orphans were adopted by Dentwil, the owner of the Trans-World Shows which was basically an intergalactic traveling circus. This was also where they first met Gleek the monkey. Growing up in the circus, one day they asked what their future held and were surprised to hear they were to live out their lives as performers. Until they turned 20, they had no rights under the laws of Exor.
Soon they also discovered that the other performers got paid yet they did not. Secretly practicing on improving their powers, they "convinced" Dentwil that he owed them quite a bit. Flying back to their homeplanet, they discovered Grax's plans to destroy Earth and embarked on their mission in which they first met the Super Friends. Most importanlty, they learned that
"people with special powers can be other than carnival freaks, they can be super-heroes!"
Despite being runaways, the Twins returned to Exor with the Super Friends to help capture two super-criminals. As thanks, the Twins received word from the Grand Rulers that they were now free of their obligations to Dentwil. (Gleek was also allowed to stay with them).
As thanks for their help, the Justice League arranged for the teens to live with a scientist under the names Johan and Johanna, as exchange students from Sweden.
In 1995's Extreme Justice #9, once again, a spaceship crashes on Earth. Zan and Jayna arrived in the current DC Universe, once again on the run. This time, things seemed more dire. Tired and hungry, they found their way to the nearest gas station. Immediately they were threatened and exhibited their powers in self defense. After the local law enforcement made matters worse, the Extreme Justice team met up with the two aliens. It's revealed that the Twins were slaves of a evil alien slavelord.
With the help of Extreme Justice, they were able to prevent their race from being sold into slavery. Zan and Jayna choose to stay on Earth with Extreme Justice in issue #16.
The Wonder Twins haven't been seen too much lately. They did pop in to hang out with Young Justice for a few issues. two made an appearance in Young Justice as well.
The twins have been referenced countless times in various tv shows, their odd powers and campy look easy fodder for comedy, and quality memories for old school superhero fans. They have also made appearances in several shows, including a statue in Justice League, and a recent appearance on Smallville as themselves.
In Justice League Unlimited, there were analogues of the Wonder Twins named Downpour and Shifter. Downpour, based on Zan, had the power to turn into any form of water. Shifter, based on Jayna, had the power to take the form of any animal. Both were members of the government-made team the Ultimen. When the Ultimen, minus Longshadow attack the Justice League, both Downpour and Shifter are quickly knocked out by Aquaman. Both twins were voiced by Grey Deleslie.
In season nine of Smallville, Zan and Jayna, played by are two "metahumans" who idolize the Blur(Superman), and do vigilante heroism to give the Blur a good reputation.