Verified answer

Khan only showed up in one episode - 'Space Seed' (episode 22 says Google.)

There are also a pair of Star Trek novels that detail the rise and fall of Khan and the others, but you should also watch 'Assignment Earth (episode 55) first.

Space Seed from Season One is the only time he's seen or mentioned in The Original Series.

He returns in The Wrath of Khan.

He is mentioned, several times, in the Enterprise storyline that deals with the Augments (Borderland, Cold Station 12, and The Augments).

I do not even comprehend the place to begin! My favorites are the ones that ask questions on human history... Patterns of drive Bread and Circuses the town on the threshold of ceaselessly however, i'm sucker for McCoy, so my favorite favourite is "For the arena is hole and i have Touched the Sky" ...Oh I almost forgot The Cloud Minders and The Empath too. Do not make me select!! :)