T'other day on TCM, I caught a bit of Shatner's big-screen debut in
The Brothers Karamazov with Yul Brynner, Joseph Cotten, and Lee J. Cobb. He played a very quiet, pious character, the youngest brother. In the parts I saw, he was mostly standing around in the background while the bigger stars were talking, or facing away from the camera while talking (or mostly listening) to Brynner.