Who played the shy science teacher on the 1950s U.S. sitcom "Mister Peepers"?

I remember him from the animated TV series "Underdog" as well as his appearance on The Twilight Zone.

Also the voice of the underdog cartoon too!!

TWeezyA, yes. He played a hit man in a Man From Uncle episode.

I remembered reading about him after his death from his wife. She greatly steamed him and loved him very much. He was very kind and gentle, she said.

miss him now!!