L%26O_SVU_PROMO_29_APR_08.jpgIt may be hard to believe, but tonight’s episode of Law and Order: Special Victims Unit (10:00 p.m., WNBC 4) is the 200th episode for the first of the Law & Order spin-offs.

One big difference between SVU and the mother ship is how the show over nine seasons has gone though only minimal cast changes, with the four regulars - Christopher Meloni as Elliot Stabler, Mariska Hargitay as Olivia Benson, Richard Belzer as John Munch, and Dann Florek as Don Cragen - there since day one. And the show's appeal is global: There's even a a Russian version!

Tonight, Robin Williams guest stars as a psychopathic engineer manipulating Benson and Stabler in this milestone episode. Given Williams' track record, it's unclear whether he'll be annoying (see this and this for the range of criticism) or perfect as a creepy scary freak role (the way he was in One Hour Photo). With luck, the annoying Williams will not show up tonight.

This isn’t the first time an actor better known for comedic roles has appeared as a guest star on the show--Jerry Lewis played Sgt. Munch’s mentally ill uncle last season--nor is it the first time Williams has guest starred on a police drama starring Richard Belzer as John Munch (he guested on an episode of Homicide: Life on the Street in 1994).