The phrase "core cast" refers to the main group of actors or characters in a movie, TV show, or play who play the most important and central roles in the story. Full definition
What it lacks in a strong villain it more than makes up for with a likable core cast. (toucharcade.com)
It's a nice vote of confidence for creators Max Mutchnick and David Kohan, as well as returning core cast members Debra Messing, Eric McCormack, Megan... (avclub.com)
Only Defiance, of all games, has managed to maintain a consistent core cast from beginning to end, and I felt it gave the world and story a texture that most MMOs lack. (mmobro.com)