I’ve been watching the western anthology series “Death Valley Days” the past six weeks. I was startled to see Clint in a small role in “The Last Letter” episode which aired Dec 8, 1956. He appeared in a couple of TV shows in 1955, so this was among his earliest acting gigs.
This looks like his first role and was uncredited.
Clint Eastwood’s 1st Movie Role in “Revenge of the Creature” 1955
https://www.youtube.com/watch?v=rKCr5wvI4TY
I just watched his first appearance in a 1956 TV Western where he played a young U.S. Calvary lieutenant. It was in a fairly obscure western called "Cochise, Greatest of the Apaches."
He’s shown up in some oddball places. He had a guest appearance on the Mr. Ed show, which means he appeared with both a talking mule (Francis in the Navy) AND a talking horse.
There’s also a photo of him ordering french fries at Palisades Park, NJ.