Professor Callahan is the secondary antagonist in the 2001 comedy film Legally Blonde and its 2007 Broadway musical adaptation.
He works at Harvard University and is the former teacher of Elle Woods. While initially seen as a respectable lawyer and mentor, Callahan is eventually revealed to be a perverted man who enjoys sexually harassing women so he can sleep with them, hiring Elle on his internship solely so he can seduce her.
After Elle Woods was dumped by her boyfriend, Warner Huntington III, she decides to attend Harvard Law School to prove him wrong. However, Elle is having trouble fitting in, as the students and environment at Harvard were different to her. She is given an internship in Professor Callahan's class, where she gets to aid Professor Callahan on a recent murder case regarding the murder of Brooke Taylor-Windham's husband Hayworth, who was fatally shot.
Callahan first appears to be impressed with Elle Woods because of her surprising intelligence in deducing that Enrique Salvatore (who lied when testifying that he had an affair with Brooke) was gay and exposing the fact to the courts and weakening the case against Windham. But when he asks Elle to talk to him alone in a room he hits on her, which makes Elle realize he was only impressed with her because he wanted to sleep with her, which causes Elle to leave the room, while Vivien (who heard part of their conversation incorrectly assumed that Elle willingly had sex with Callahan to allow her a spot on the case) angrily asks Elle why she doesn't just sleep with the jury, causing Elle to nearly quit Harvard and go home. However Elle is inspired by her friend Paulette Bonafonté and Professor Stromwell to return to the case. Meanwhile, Emmett Richmond, Callahan's junior partner, tells Brooke and Vivien about what Callahan did and Brooke fires him and replaces him with Elle, who discovers that Chutney Windham is the real killer, wins the case and gets Brooke exonerated of all charges. Callahan is eventually fired from his firm and the School. A few deleted scenes on the special DVD has one where there was a report that Chutney committed suicide in prison on the morning of Elle's Graduation. Also in the same prison facility, Enrique is serving time in prison for committing perjury in Brooke's trial along with his new cellmate, Professor Callahan, who was sentenced to prison for raping one of his female students and interns.