QUOTE(Matthew Winn @ Mar 25 2008, 04:39 PM)

Steven Wayne was in Cats from its opening through to October 2000, spending 19½ years in the show. He played more than one role, although in that show it doesn't make a heck of a lot of difference given that only someone who knows the show well can tell the roles apart.
I think Carole Ball was in Me And My Girl for its entire run and, I suspect, played the same role throughout. Not quite the same but Kevin Amos was the Musical Director of 42nd Street at Drury Lane for the entire run of, what, 4 or 5 years. And some members of the orchestra at Phantom have been there since it started.