Hmmmm... I don't think he ever had a role on ST-TOS. Could you be thinking of Mark Lenard? The actor who portrayed Spock's father Sarek.
Andreas Katsulas will be missed.
"I believe that when we leave a place, part of it goes with us and part of us remains. Go anywhere in the station, when it is quiet, and just listen. After a while, you will hear the echoes of all our conversations, every thought and word we've exchanged. Long after we are gone .. our voices will linger in these walls for as long as this place remains. But I will admit .. that the part of me that is going .. will very much miss the part of you that is staying."
G'Kar to Sheridan, Objects in Motion