Beam me up Scotty is an iconic Trek phrase yet it has never been actually uttered. When iconic means 'public image' I couldn't care less about it, especially when I can have the real thing instead of a distorted image of it.
Which is not the sense of the word I employ. "Iconic" as in embodying and exemplifying the traits of a person, place or thing.
Khan is iconic because he is one of the seminal depitctions of a classic Trek "villain": one who is not wicked for wickedness' sake, but rather simply out of step with the rest of the world around him. Dangerously so in effect, but not because he was an inherantly
evil person.
I quote this from the original "Space Seed".
SCOTT: I must confess, gentlemen. I've always held a sneaking admiration for this one.
KIRK: He was the best of the tyrants and the most dangerous. They were supermen, in a sense. Stronger, braver, certainly more ambitious, more daring.
SPOCK: Gentlemen, this romanticism about a ruthless dictator is
KIRK: Mister Spock, we humans have a streak of barbarism in us. Appalling, but there, nevertheless.
SCOTT: There were no massacres under his rule.
SPOCK: And as little freedom.
MCCOY: No wars until he was attacked.
SPOCK: Gentlemen.
KIRK: Mister Spock, you misunderstand us. We can be against him and admire him all at the same time.
There were many things to admire about Khan, while at the same time acknowledging the danger he represented.
Khan is not a villain? Of course he is and on top of that he is the evil equivalent of Superman (he is quite literally a superman) and not Batman, evil by design and not by choice.
No, he was designed to be physically and mentally superior, which fostered superior ambition. This is Khan as we know him prior to his exile on Ceti Alpha V.
Once there, given what happened to him, his superior intellect may have made it technically possible for them to survive, but being "beaten" so conclusively by his environment was more than his inflated ego could handle, and he snapped.
His role in TWOK is to trigger something in Kirk and if you take away Montalban and focus merely on the text he isn't all that interesting. Given the character setup this is hardly surprising.
His role in TWOK is to represent Kirk's history (paralleling the David plot arc), catching up to him as he ages.
Khan in his intrinsic qualities and his role in both stories he is in is the embodyment of elements of classic Greek tragedy.