How many of the original cast members of Law and Order remained with the show for its entire run?

Only one original cast member, Jerry Orbach, who played Detective Lenny Briscoe, remained with "Law & Order" for its entire run from 1990 to 2010. Other original cast members, such as Sam Waterston and S. Epatha Merkerson, joined later and stayed for significant portions of the series, but none were part of the entire 20-season span. The show is known for its rotating cast, with many actors coming and going over the years.