Sometimes (though probably erroneously) credited for inventing the "fist bump," the Wonder Twins first activated their powers in 1977 on the All New Super Friends Hour, the show for which they were created. The duo were created as replacement sidekicks to the Justice League AKA Super Friends for the non-powered teens Wendy and Marvin. The twins were subsequently adopted into the comic books.
When the two bumped knuckles, Zan (the male twin) could take the form of anything made of water. He could be anything as simple as a rain cloud or ice cube to a fully functional ice rocket. Most of the time, he just turned into a puddle of water and rode around in a bucket. Jayna (the girl twin) could assume the shape of any animal from dinosaurs to dragons to gophers. Her favorite seemed to be an eagle, a form she would use to carry around her puddle brother. Oh and they had their own sidekick - a "space monkey" named Gleek.
They were always coming up with ridiculous ways to use their powers, like burrowing a moat to stop a grizzly. Note in the picture, Jayna is the gopher, not the bear.
Elephant / ice bridge was another fun combo.
As was squid / ice boat.
After Super Friends, the duo were gone but not forgotten. They could be spotted by a keen eye in statue form cameoing in an episode of Justice League.
The Justice League Unlimited run paid homage to the twins as well as the "ethnic heroes" (sans El Dorado) that were created for Super Friends. The Ultimen were a government created team of heroes built as an contingency plan in case the League ever went rogue. Downpour and Shifter were wussy purple clad twins with powers very similar to those of the Wonder Twins.
Well, just like Speedy, Metallo, and Hawkman, the Wonder Twins is a coming to Smallville this season. The episode Idol will show the two fist bumping away with their signature purple attire. Hopefully, no bears will attack. No word yet on Gleek.
Lastly, here is a look at Adult Swims comical remixing of the classic "Gopher Moat" rescue.