1. Warren Christopher
Episode He's Referenced In: Homer's Phobia, Season 8, Episode 15
How He's Referenced: Moe blames him for turning an entire generation of kids gay by ensuring that they'd never have to go off to war.
Who He Was In the Real World: Warren Christopher was Bill Clinton's first Secretary of State, serving from 1993-1997. According to his Wikipedia, he helped in negotiating the deal that ended the Bosnian war, meaning that Moe's assertions about him being responsible for a lack of wars wasn't that far off.
How Obscure Was The Reference: Honestly, at the time it probably wasn't all that obscure at all. He would have been a fairly well known political at the time the episode aired. That said, as time has gone on, his legacy hasn't burned as brightly as some of the Secretaries of State that followed him.
2. Ray Bolger
Episode He's Referenced: When You Dish Upon a Star, Season 10, Episode 5
How He's Referenced: After he's fired by Alec Baldwin and Kim Basinger, Homer goes on a crusade against all celebrities. In a long tired against famous people, he uses Bolger as a touchstone of Hollywood elitism and selfishness.
Who He Was In The Real World: Ray Bolger is actually the actor who played Scarecrow in The Wizard of Oz. He never had a role quite as big (obviously) but it sounds like he had a respectable enough career. At one point, he even had a TV show named after him.
How Obscure Was The Reference: Given that he was the star of one of the most iconic movies ever made, not very. That said, though he definitely left his mark on the world, Bolger's name was a little lost to time. In any case, he's a very out of the blue celebrity for home to pick in this context, particularly as he would have been dead for 11 years by the time the reference was made.
3. Charles Kuralt
Episode He Was Referenced In: Homer The Great, Season 6, Episode 12
How He's Referenced: In trying to dissuade Homer from stalking Lenny and Carl, Marge makes reference to the time Homer apparently stalked Kuralt under the suspicion that he had dug up his lawn. Homer's logic: "Well, something did!'
Who He Was In The Real World: Kuralt apparently had a long running segment on The CBS Evening News, which essentially involved him traveling the country in a RV and shining a light on parts of America that might not normally make it onto the evening news. After that, he because the anchor of the CBS Sunday Morning News.
How Obscure Was The Reference: This is another case where even if Kuralt wasn't the most obscure person on this list, the fact that he is the person used in the context is extremely out of left field. It's a rare instance where understanding a reference actually makes the joke feel even more confusing and random, which is pretty cool.
4. James Coco
When He's Referenced: Treehouse of Horror IV, Season 5, Episode 5
How He's Referenced: A demon in hell attempts to dole out some ironic torture to Homer by force feeding thousands of donuts. When Homer ends up enjoying it, the confused demon says that the same punishment had very quickly driven Coco insane.
Who He Was In The Real World: He was pretty much just a character actor. He was nominated for an Oscar for a movie I've never heard of called Only When I Laugh, and seems like he had a pretty solid career all things considered. Based on his filmography though, I'd say the most likely role someone reading this would recognize is his cameo in The Muppets Take Manhattan.
How Obscure Was The Reference: Seems fairly obscure to me. He had a lot of roles, but he doesn't seem like he would have been a household name at the time of the episode's release, particularly as he had been dead for 6 years by the time the episode was released. On that note, though, doing research on Coco and learning that he died of AIDS at the age of 56 makes a joke about him being tortured in hell feel a little darker than I would have expected.
5. Gabby Hayes
When He's Referenced: Radioactive Man, Season 7 Episode 2
How He's Referenced: When Milhouse is cast as Fallout Boy in the movie adaptation of Radioactive Man, the director and producer of the film feel like they have a star on their hands. In their excitement, they compare Milhouse's potential for success as that of Gabby Hayes.
Who He Was In Real Life: He was another character actor who got famous by playing the grizzled old sidekick in cowboy movies. From the looks of it, he helped create the gnarled old prospector archetype you see referenced in movies like Toy Story 2.
How Obscure Was The Reference: Fairly? Hayes has an impressive filmography, and I have no doubt that huge cinephiles would instantly know who he is. That said, he's hardly the gold standard of a Hollywood celebrity....which I guess is kinda the point of the joke to begin with.
6. Rory Calhoun
When He's Referenced: Two Dozen and One Greyhounds, Season 6, Episode 20
How He's Referenced: When Mr. Burns steals Santa's Little Helper's puppies, he becomes enamored with a dog who has the ability to stand on its hind legs. He then likens the puppy to Rory Calhoun because they're both always standing, and subsequently names his new pet Rory.
Who He Was In Real Life: He was an actor. He starred in a lot of Western films that I've never heard of and his face is wholly unrecognizable to me.
How Obscure Was The Reference: Very. Calhoun's own Wikipedia has an entire section dedicated to his reference in The Simpsons. Clearly the writers were trying to come up with the most obscure random person they could think of, and they succeeded.