Case in point: His Iago in the Olivier 1965 "Othello" is the best I've ever seen. Here's a link to a clip -- it's worth watching if only for the scenes between Olivier's Moor and Finlay's Iago. His demeanor is so consistently sincere, direct, and without affect (a wonderfully sociopathic interpretation) that every time I see it, I still ca't tell if he's telling the truth or not! Deadly understatement all the way. Brilliant.
And, oh yes, he makes me laugh so hard I hurt myself. He is a wonderful, buffoonish Porthos in the Richard Lester Musketeers film trilogy.
He famously (in England) played the lead in Dennis Potter's "Casanova":
And is quite simply the best Jacob Marley to date.
Other highlights -- a memorable Dogberry, a notable victim in "Twisted Nerve," the villain in "Shaft in Africa," Lestarde in "Murder by Decree," Dr. Fallada in Tobe Hooper's cosmic vampire mess "Lifeforce," and the father in "The Pianist." A thoroughly enjoyable performer, every time. It looked as if he was having fun.