One of my absolute favourites. I first noticed him in Flash Gordon as Ming, but in the early eighties he was in quite a few big commercial films: Escape to Victory, Conan the Barbarian, Never Say Never Again, Dune, Ghostbusters 2.
Like Christopher Lee, a lot of his parts are quite small, so he appears in a high number of films.
My favourite part is inspector Ulisse Moretti in Sleepless. A detective who's plagued by his failing memory about an old case.
I never realized in The Exorcist he's in make-up too, not just Linda Blair - he was only just over 40 there. It took three hours to transform him into an elderly priest.
He didn't do a whole lot of horror though, despite The Exorcist's success. He seems to gravitate more towards thriller, sci-fi, fantasy, war, history and drama of course. Also some comedy.
It's also hard to take him as purely evil. Even in Needful Things he's quite likeable - he seems to genuinely enjoy giving people their precious belongings back. Even if he plays people against each other, as individuals he helps them.
He's just too avuncular looking to play evil characters. You have to totally transform him for that, like in Flash Gordon.
Solomon Kane (2009) is another film I really love and highly recommend.
He also has a cameo in The Wolfman remake director's cut (2010).