This is what I found and is wrong:

According to the Star Trek Wiki Memory Alpha, Michael Dorn appeared in 5 movies and 272 episodes as Worf. The second place is held by Colm Meaney, who has appeared in 211 episodes, and is also the only actor to have appeared in the pilots and finales of both TNG and DS9.

When you include actors that appeared in episodes as voice only charactors, Dorn was out played. Acording to the web site IMDB, which lists all roles she (and other actors) has been in for her entire carrer, the correct answer is Majel Barrett.

She appeared in the original pilot as the first officer (Number 1) and in the origial series as nurse Christine Chapel (34 episodes). She was in the 1970s cartoon series with voices from the original cast (21 episodes). She appeared in TNG as Dianna Troi's mother in some episodes and also as the voice of the computer (96 total). She was in ST DS9 as the computor voice and as narrator in a couple of episodes (30 in all). She was in ST Voyager as the computor voice (114). She was in ST Enterprise, 2 episodes, as computor voice. She was in one episode of a series I have never heard of till today called ST New Voyages:Phase II as a computor voice. She was in a total of 298 tv episodes.

She also was in a total of 6 movies as Chapel in the earlier movies and computor voice in the later movies. Her last movie was Star Trek released in 2009. She also provided the voice for numerous video games. She died in 2008.