Lists by TheFirstWave
Voice acting is included, but made-for-TV films, straight-to-video releases, and video games are not - only Hollywood theatrical releases.
(I say 'Hollywood' because I'm not really delving into Bollywood, Hong Kong cinema, or other non-U.S. film industries. Nothing against them, I just don't know them as well.)
Actor does not have to appear in all films of a series, or even 3 films consecutively to be counted: As long as he or she has been in 3 or more films in 2 different series, it counts.
Actors are listed chronologically by when they joined this club - based on release year of their second threepeat, which is included in parens.
I'm not as knowledgeable about films from the 70s and earlier. Did I leave anyone off, or make any other mistakes? Please comment below if so. Thanks!