In the Star Trek episode "What Are Little Girls Made Of?" Kirk finds out that Dr. Korby wants to perfect humanity by replacing humans with androids. The two have the following exchange:
KORBY: What you saw was only a machine, only half of what I could've accomplished. Do you understand? By continuing the process I could've transferred you – your very consciousness – into that android. Your soul, if you wish. All of you. In android form, a human being can have practical immortality. Can you understand what I'm offering mankind?
KIRK: Programming. Different word, but the same old promises made by Genghis Khan, Julius Caesar, Hitler, Ferris, Maltuvis.
Why didn't Kirk mention Khan as part of this list? I'd assume that one of the most prominent figures of the Eugenics Wars – and one having been prominent more recently than the three non-fictional characters in the list – would be a prime example for Kirk, especially given how strongly characters associated with the Federation throughout the franchise react to ideas related to improving humanity through scientific augmentation – because of the Eugenics Wars.
Clearly, the character of Khan had not yet been invented by the time this episode was written, but I'm wondering if there's any in-universe explanation for this omission.