Not exactly sure who you are referring to but the fairly well-known character actor Walter Burke died in 1984 at the age of 75. Neither Memory Alpha nor IMDB show him having ever worked on Trek. Nor do the credits for that episode list him, nor is there a speaking part that doesn't have an actor attached to a role. So are you talking about
another Walter Burke who
also died in 1984 who had a non-speaking role in that episode? Also if he died in 1984 at age 94, he would have been 78 years old in 1968 -- would Dr. McCoy/M'Benga have had a 78 year old assistant on their staff?
This is the well-known Walter Burke.....
Known for: Support Your Local Sheriff!, All the King's Men, The President's Analyst
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