Rouge the Bat is a jewel thief who was transported to earth with Sonic and friends when Dr. Eggman caused Chaos Control. The President has her arrested and then asked to become a government agent, she agrees and makes good friends with another government agent named Topaz.
Rouge is rather flirtatious, especially with Knuckles, whom she has a crush on. She seems to take pleasure in teasing Knuckles and seeing him blush. She also doesn't seem to be offended by Knuckles's insults toward her, such as when he calls her batty (which he does quite often). She will likely take advantage of other peoples' kindness, though she sometimes manages to pay them back. She is extremely hard to figure out, and uses this to her advantage; it is hard to understand if she is on Sonic's side or on Eggman's. She can usually be seen with a smirk on her face.