I'm gonna mention John Cazale because the guy really deserves the recognition. If he hadn't died so young, I think he'd be considered a master.
"I wanted to be a wife so that I could have been her real mother. I wanted to be a boy so that she could be in love with me. I wanted her to be my full sister instead of my half sister. I wanted her to be a slave so that I could set her free and make her rich."
My list was based on 4 things : actors I found the best (where possible)/historically important either for films or in themselves/uniqueness/and lastly personal preference - in that last one, it tilted strongly American.
At a certain point it stops being about just the best - there's a level of actors outside the absolute best to me that are just too close to call or they are too similar or of equal importance or that I have no strong preference for either.......but Cazale to me is a no brainer for the list.
He was great sure, every film he's in is historically important too, and HE'S historically important too - that's what gets him over. He's unique and special, as an actor "type" he basically defined playing weak on screen - he set the model for many later great actors and performances like PSH and Sean Penn in some of his less overtly masculine stuff (Falcon and The Snowman for one).
Love him and I could watch him all day......
And when pacinoyes saw the breadth of his domain, he wept, for there were no more worlds to conquer
Speaking of under the radar - too young to be a part of the great 70s generation, but too established to be a part of the 80s generation - even though by that time that his career took shape, he was better than (almost?) all of those 80s guys. FYC Jeff Bridges