James Cagney is a great example of how to wear classic clothes like double breasted three-piece suits with ease.
David Niven for how to wear clothes with class.
Yul Brynner as a man whose clothes were the perfect background - always appropriate but never conspicuous. Brynner turned what would have otherwise been a weakness - baldness - into a strength.
Henry Silva, the character actor who was always perfectly turned out in any of his roles.
Ronald Reagan - I read that Reagan was so conscious of how a suit appeared that he'd take off his suit pants and put on jogging pants while still wearing the rest of his suit during flights on Air Force 1 so that his pants would still have a sharp crease for when he arrived wherever he was going. Apparently it drove Nancy crazy
Even when Reagan was on his ranch clearing brush, he still looked the part. The man never had a sour note, brown suits and all.