"The Savage Curtain"
Star Trek (the original series)
If things had gone differently, "Savage Curtain" would be known for featuring Abraham Lincoln, and pretty much only that. There's a lot of mileage to be had from Lincoln, and the original series had a habit of using every possible story template as a springboard for Kirk's adventures.
But things went as they did, and Lincoln was overshadowed by a couple of dudes named Surak and Kahless.
Who are those dudes, you ask (you Star Trek neophyte, you!)? They were both founders of the way famous Star Trek alien civilizations tend to behave: Surak instituted Vulcan logic, Kahless laid the foundations of Klingon honor. Kahless made an appearance in Star Trek: The Next Generation ("Rightful Heir"), or at least his clone did, and his chosen weapon, the first bat'leth, was fought over in Deep Space Nine ("The Sword of Kahless"). Surak's teachings were reawakened in Enterprise ("The Forge"/"Awakening"/"Kir'Shara").
So "Savage Curtain" is known for introducing these fine dudes.