Blackfire

Blackfire is Starfire and Wildfire's older sister, the firstborn princess, and eldest daughter of the long-dead King and Queen of Tamaran. She is the former Grand Ruler/Empress of Tamaran. She serves as Starfire's arch-nemesis.

Background
Blackfire first appeared when she arrived on Earth in the second episode Sisters. She gave Starfire a centauri moon diamond and pretended to enjoy being reunited with her. Blackfire won the Teen Titans' support by having fun with them and telling them stories of adventures she had throughout her travels in the galaxy.

The Titans seemed to like her so much, Starfire was beginning to think they wouldn't need her around anymore. She was especially unhappy with her sister's attempts at flirting with Robin. When Starfire thought of leaving Earth, the Centauri Police showed up and captured her. The Titans rescued her and explained to the Centaurians that they have captured the wrong Tamaranean. The Titans then discovered that Blackfire had framed Starfire for crimes by giving her a stolen jewel from the Centauri System. Blackfire, who was leaving Earth at that exact moment, was defeated by Starfire after her right hand was hit by Starfire's starbolts. She was about to attack again however, the Centauri Police catch her from behind and she's taken to prison, swearing revenge on her little sister for shaming and humiliating her.

Blackfire later broke out from prison and wrested control of Tamaran as its new Grand Ruler. Blackfire attempted to get revenge on Starfire by forcing her to marry Glgrdsklechhh, a hideous alien. This was actually part of an elaborate plot between Blackfire and Glgrdsklechhh; by marrying Starfire to Glgrdsklechhh, he would reward Blackfire with a very powerful jewel. When her ruse was uncovered, Blackfire was once again defeated by Starfire in an official challenge for the throne and banished from Tamaran by her sister's royal decree.

Blackfire was one of the only villains missing from the lineup of the Brotherhood of Evil, suggesting that she was not out to get all the superheroes, or even the Titans, but simply to just take out Starfire.