Tomorrow Is Yesterday: The Enterprise is thrown back in time to 1960s Earth.

Space Seed: While on patrol in deep space, Captain Kirk and his crew find and revive a genetically-engineered world conqueror and his compatriots from Earth's Twentieth Century.

Adorable that the 60s had so much faith in the future of humanity and also the space program

Granted, maybe it still happened, and a bussard ramscoop-powered sleeper ship was out encountering the people of Alpha Centauri at the same time WWIII was raging back on Earth.

Ricardo Montalban as Khan Noonien Singh in the Star Trek: The Original Series episode Space Seed.

Even to this day, it's hard for me to wrap my head around the fact that this is the guy who first sang (with Esther Williams) the Academy Award-winning song (and Christmas-time perennial) Baby It's Cold Outside in the film Neptune's Daughter (1949).