Red X

"I created Red X. Every System, every weapon."

- Robin

Red X is a former villian of the Teen Titans.

Origin
Red X started out as an Evil Alter-Ego of Robin so he could get close to Slade and what he was planning, but in a later season, someone stole the Red X suit and decided to wear it and become a thief.

Red X (Robin)
When the Teen Titans first encountered an army of Slade's Robots, Robin want to figure out who he was, and what he was planning. So he created an Evil Alter-Ego to figure out Slade, but in the process, Robin almost crossed the line between Good and Evil, and almost lost his friends.

2nd Red X
After Robin quit being the Red X, the suit was never seen for some time. Until someone stole the suit and decided to wear the suit and become a thief. He only stole stuff so he could look out for Numero Uno. But when Raven, Cyborg, Starfire, and Beast Boy were kiddnapped by Prof. Chang, Red X decided to help Robin take out Chang. But he only did this to steal the Xenothium to power up his suit. However Robin excepted this so he manage to take Red X's belt. X manage to the Xenothium to cause a distraction and manage to escape from the Titans.

Red X made another appearance, when Ding Dong Daddy manage to steal something precious from Robin.Because it was valuabe yo Robin, all the Teen Titan villains teamed up and tried to steal it from DDD, while preventing the Teen Titans from getting the Briefcase, including Red X. However near the end of the episode, Red X saw in Robin's eyes that it was really valuable to him and decided to take out the other villains that wanted the briefcase.

Trivia

 * It's been hinted whether or not Red X really is Jason Todd, Robin's adopted brother