Michael Dorn(I)

Made a grand total of 282 "Star Trek" appearances. He appeared in 175 of the 178 episodes of Star Trek: The Next Generation (1987), 102 of the 176 episodes of Star Trek: Deep Space Nine (1993) Rotta verso l'ignoto (1991), Generazioni (1994), Primo contatto (1996), Star Trek - L'insurrezione (1998) and Star Trek - La nemesi (2002). He also directed the following episodes: In the Cards (1997), Inquisition (1998), When It Rains... (1999) and Two Days and Two Nights (2002). The 277 episodes of Star Trek he appeared in means he has appeared in more episodes of Sci-Fi Television than any other actor.

But now they have the series down to a real science where it's about an hour.