 In 2007, Alexander was a guest star in the third episode of the improv comedy series "Thank God You're Here".He has been a frequent guest and panelist on Bill Maher's "Politically Incorrect" and "Real Time"; "Hollywood Squares"; the "Late Late Show", with both Craig Kilborn and Craig Ferguson; and the "Late Show with David Letterman".In 2008, Alexander guest-starred in the season four episode "Masterpiece" of the CBS show "Criminal Minds" as Professor Rothschild, a well-educated serial killer obsessed with the Fibonacci sequence who sends the team into a race against time to save his last victims.