Modern Greek: like everyone else said, ηθοποιός. In Ancient Greek this meant “character-building”. The modern meaning came about because plays can be character building, I suppose, but I can’t find out when the meaning shift happened. Pretty sure it’s very recent.
The word is from katharevousa. The old vernacular word is θεατρίνος, which is still around in its pejorative meaning of “drama queen; impostor”.
Like the Ancient word for actor.
Oh, what’s the Ancient word for actor, you ask?
You recognise that word, don’t you?