Arguably the biggest breakout star of the show, Raven is anything but sociable, but she's also one of the biggest aces in the hole for the Teen Titans.
Raven is the literal daughter of a demon, in this case, Trigon. Her life was made so that he could be freed from a prison. Despite this, her mother whisked her away to monks on the planet Azerath, and trained her to become something better. Upon joining the Teen Titans, she has worked hard to overcome her destiny, and in fact, she did it.
But...that only happened after being forced to lower her barriers to her friends. As noted, Raven isn't the most social girl. She prefers nothing more than to be alone mediating, and she doesn't like when the other Titans try and force her to do things with them. And yet, Raven does know compassion, she is there to comfort them at times when things are bad, and she is their friend through and through.
Raven is also a mystical powerhouse. She's an empath of sorts, can use spells to teleport, move objects, even project her mind into someone elses. All her power though is tied to her emotions, which is why she tries to keep them in check when she can.
Still though, Raven is a worthy member of the Titans, and has proven her value time and time again.