Uncle Clyde was played by Len Carlson.
Lydia's uncle on her father's side of the family, in fact, he's Charles Deetz's big brother. Clyde is a farmer who prefers the good old days before freeways and remote-controlled "electric do-dads". Apparently, he's the one where Lydia got her love for insects.
"Back home we have nothing better to do then sit around and listen to crickets in our pajamas, and we like crickets in our pajamas... We like 'em just fine."
Uncle Clyde means well and seems to be pretty relaxed next to Charles (probably because he was never exposed to the city life), but Lydia gets scared (and somewhat embarrassed) whenever somebody says the word "fun" around him, for his idea of good-old-fashioned-fun is to give a ventriloquist act with his dummy named "Beppo", and Uncle Clyde is by far the worst ventriloquist that even Beetlejuice (as Cousin BJ) had ever seen, not only because of corny, played-out jokes, but because Clyde's lips move whenever "Beppo" says his lines! (BJ possessed the puppet to improve the act.)