TOS fans know him as Nils Baris from "Tribbles." DS9 fans know him from "Sanctuary."
But I just read his wiki biography, and good freaking lord, what a fantastic career for this 90-year-old character actor. Seldom starring, appearing mostly in supporting roles, he continues to perform -- I caught a radio interview with him last week.
I am just absolutely amazed. For an actor to move from series to series over decades, and never detract, never draw undue attention to himself but instead always perform in service of the story -- well, that is a very, very fine actor, indeed.