Man ... Paths of Glory, Spartacus and 20,000 Leagues Under the Sea. That's a hell of a career. Oddly enough, as a kid, I was introduced to his acting in "Tough Guys" with Burt Lancaster and loved it. I haven't seen it in 30 years, and it's probably far more terrible than I remember, but that was the movie that made me seek out more of his work.
20,000 Leagues Under the Sea was the next one I saw. My Nana used to babysit my sister and I on Friday nights (overnight), and on Saturday mornings we would watch a show called Dialing for Dollars with George Allen. It showed all kinds of old sci-fi movies, like The Blob, Planet of the Apes and such. That's when I saw 20,000 Leagues.
I knew I liked him, but it wasn't until college that I saw Paths of Glory and Spartacus and that was a whole new level. The guy was great. And his son was no slouch either. Hollywood royalty. RIP.