After his film debut , '' Krush Groove '' , Underwood 's 1985 appearance on '' The Cosby Show '' landed him a short stint on the ABC soap opera '' One Life to Live '' as Bobby Blue , which eventually led to his performance on the TV series '' L.A. Law '' , where he appeared from 1987 to 1994 . In 1996 he was featured in the July issue of '' Playgirl '' . Blair also appeared in the 1987 's TV series 21 Jump Street aside a young Johnny Depp on episode " Got ta Finish the Riff . " Underwood 's film career began with roles in '' Just Cause '' ( 1995 ) , '' Set It Off '' ( 1996 ) and '' Deep Impact '' ( 1998 ) . He also had a supporting role as a geneticist in '' Gattaca '' . In 2000 , he played the lead role in the short-lived television series '' City of Angels '' . In 2003 , he guest starred in four episodes on the HBO series '' Sex and the City '' playing Cynthia Nixon 's love interest . In 2004 , he played the role of Roger De Souza opposite Heather Locklear in NBC 's '' LAX '' . He gained acclaim as the sexy grade school teacher in the CBS sitcom '' The New Adventures of Old Christine '' opposite Julia Louis-Dreyfus for two years . In 2007 , he guest starred in an episode of the NBC series '' Law & Order : Special Victims Unit '' . He played the character Alex in the first season of the HBO series '' In Treatment '' , for which he was nominated for best supporting actor at the 2009 Golden Globes
2009 Golden Globes
66th Golden Globe Awards
Blair Underwood