He was once a friend of WordGirl's known as Professor Steven Boxleitner, a kind, but easily distracted scientist. He made a device that was supposed to help people read into the minds of rodents. While doing this experiment, he was hooked up to a lab rat named Squeaky. When Boxleitner wasn't looking, Squeaky pushes a button which said "Holy Cow! Don't Touch This Button!" and the result fused his mind with Squeaky's. This causes Dr. Two-Brains to come into being. Still, on occasion, WordGirl does try to tell him to fight the other brain, to no avail. Dr. Two-Brains' main motive is to steal cheese in most of his appearances or threatens to turn the entire town in cheese. As a villain in this show, he takes great pride in being evil, and once tried to improve on his image when a new villain took his spot for the number one villain. He's also one of the few villains who have found out WordGirl's secret identity, and uses this advantage to kidnap her and her family. He is later hit by the amnesia ray, however. Also, besides WordGirl, he seems to know most of the words in the show, and even defines a few as well. Also, because of his other brain, his weakness is being scared by cats.
Steven Boxleitner was a brilliant scientist with chestnut brown hair and dark eyes. As Dr. Two Brains, however, he has white hair and red eyes, along with whiskers and a mouse brain fused to the side of his head.
- He could be seen as the main antagonist of the television series, as he's one of the few recurring villains in the series. In addition, he actually had a personal connection with WordGirl.