Criteria is living, actor (male)=ignore politics, directing, etc.. I have to say diversity in roles is crucial.
Eastwood is like Kostner==he mostly does Eastwood (I know, Beguiled is an exception).
Kostner plays Kostner. His Wyatt Earp was "Wyatt Earp plays Kevin Kostner" more than the other way around.
I have to go with Kevin Spacey, I think. Largely based on Glengarry Glen Ross and Usual Suspects.
Actress: Helen Mirren, I think.
But, my opinion might change by tomorrow.
He spells it Costner, but his Robin Hood really upset some British viewers. Just not plausible. Errol Flynn (long gone now) was Australian-born and was a good Robin. Richard Greene on TV, less so, but okay for a typical TV show.
Sir Anthony Hopkins should be more mentioned here.
One fellow mentioned "Sir" Richard Burton. He was a really impressive actor and perhaps because he was Welsh, was chosen to read the narration in, "Zulu." (The troops in the film were from a Welsh regiment, as in real life.)
But I don't think he was ever knighted. He took the name of a famous explorer, who WAS knighted. THAT Sir Richard Burton was also an author and a skilled swordsman.
Actresses? Oh, sure: Judi Dench and Helen Mirren. Meryl Streep. ATTRACTIVE acresses? Amanda Seyfried. Lara Cox (Australian, very versatile and much better than her roles have usually let her prove, although she aced them), and (seriously) that blonde (Sharon Stone) who made her name by uncrossing her legs in, "Basic Instinct." But she really is a good actress. She just needed a movie that'd let her become famous.
My granddaughter wants to act and is taking college drama courses. I think she'll be very good. She has a good heritage. Goodness knows, I saw enough drama from her mom as a teen, ha!
I don't like Michael Douglas for more than his anti-gun stance, which applies to most actors and other celebs. But he overacts, using emotion in lieu of talent. That seems to affect other actors in his movies, too. "Basic Instinct" had a lot of unrequired drama. His bi-polar wife is an excellent actress. So far, I haven't seen her medical condition ruin her roles. (Catherine Zeta-Jones)
Kenneth Branagh is very good in roles that suit him, as in, "Henry V".
Richard Burton was good, but he also sometimes overdid the raging emotion, as when he played Marc Antony in, "Cleopatra." But, he gets extra credit for having his sword sharpened in case he or his lover and co-star Elizabeth Taylor were attacked on the set by some Italian actors and crew who were having a labor dispute during the filming of, "Cleopatra." Taylor played the title role. She told a magazine the story of the sharp sword. I forget if he had the prop sword sharpened or bought a new sword for the purpose. Taylor said that she didn't know what he thought he'd do with the sharp sword. I think Burton knew exactly what he''d do, if forced to!