1. John Travolta made his screen debut falling off a cliff on 'Emergency!'

In 1972, after moving to L.A. to pursue his acting career, a young Travolta landed his first credited television role on the second episode of the second season of Emergency!, "Kids." The soon-to-be-Sweathog plays a 16-year-old hiker who falls off a cliff. Yep, that's Barbarino lying on the ground.

2. The "Up your nose with a rubber hose" insult was originally much cruder.

The source material for the hit sitcom was Gabe Kaplan's stand-up routine "Holes and Mello-Rolls," which colorfully chronicled his formative days as a teenager in New Utrecht High School in Brooklyn. (That's the school building shown on the TV show as James Buchanan High.) Kaplan's gang of real-life Sweathogs would toss around the insult, "Up your hole with a Mello-Roll," suggesting that one stick the pictured ice cream treat you know where. Obviously, it had to be cleaned up for network television.

3. The Boston affiliate did not air the first four episodes due to racial tensions in the city.

In September of 1974, the city of Boston implemented a busing system to desegregate public schools. The mandated desegregation led to a series of riots. A year later, when Welcome Back, Kotter was preparing its premiere, racial tension was still running high in the city. The local ABC affiliate WCVB feared that a sitcom depicting an ethnically diverse classroom would stoke the flames, so it passed on airing the show. Four episodes later, Kotter was a ratings hit around the country and WCVB relented.

Image: AP Photo/Peter Bregg

4. Lawrence Hilton Jacobs released a disco-soul album in 1978.

Gabe Kaplan scored a novelty hit in 1976 with "Up Your Nose," while John Travolta scored a legitimate smash that same summer with his Top Ten single "Let Her In." Overlooked in the Kotter cast's extracurricular musical endeavors is Lawrence Hilton Jacobs, who cut the coolest record with his self-titled debut. "Fly Away (To My Wonderland)" was a minor hit on the soul charts.

Image: Discogs

5. The show would have simply been called 'Kotter' if anything rhymed with Kotter.

Former Lovin' Spoonful frontman John Sebasian was tasked with writing the theme song to a upcoming comedy titled Kotter. The problem was he could not come up with any good words that rhymed with "Kotter." So the singer penned a less specific mid-tempo number with a tinge of melancholy, "Welcome Back." The network loved the tune so much, the title of the series was changed to work in the name of the tune.

Image: Discogs

6. Vivian Vance is the godmother of theme song singer John Sebastian.

All sitcoms trace back to I Love Lucy somehow. It's like Six Degrees of Kevin Bacon.

7. The show was retitled 'The Saturday Night Boys' in Italy to capitalize on Travolta's cinema success.

In 1980, one of Italy's two national networks decided air Welcome Back, Kotter due to the global success of Travolta. The actor was still riding high off Saturday Night Fever, so the Italians renamed the series I ragazzi del sabato sera, or "The Saturday Night Boys," perhaps hoping to confuse audiences into thinking the two stories were related. Here, have a listen to the theme song, "Call Me in America" by Pop Welcome.

Image: liquida.it

8. Three spin-offs were attempted.

Only one, Mr. T and Tina, made it to air on its own. Yet that Pat Morita sitcom, set up with a quasi-backdoor pilot in the season two premiere, "Career Day," lasted a paltry five episodes on air. The Chicago-set comedy flopped minus the Sweathogs. Later that season, another backdoor pilot was attempted with "There Goes Number 5," which was planned to become a Horshack-centric spin-off titled Rich Man, Poor Man; Horshack! Oh, and the prior episode featured zero Horshack, to show the Sweathogs could live without him. They couldn't. Two decades later, Robert Hegyes (Epstein) announced that a sequel series was in the works with grown-up Sweathogs. That never materialized.

9. There was a bizarre, little-known crossover with 'Happy Days.'

Happy Days took place in the 1950s and 1950s. Kotter was set in the late 1970s. That temporal hurdle meant little to Frank Lyndon. A member of the Bronx doo-wop group the Belmonts, Lyndon crafted one of the strangest novelty songs in an era of strange novelty songs, "The Fonzerelli Slide." The 1976 disco ditty appeared on the Fonzie Favorites album from Juke Box International record (that's the cover pictured).

In what amounts to a skit acted out over a generic boogie beat, the Fonz rides his motorcycle into the Annual Sweathogs School Dance. Horshack asks Fonzie if he arrived to become the new leader of the Sweathogs, which seems unlikely, as the Fonz should be pushing 40. Lyndon performs all the voices. We'll put it nicely and say he misses the mark. It's truly one of the stranger things you'll ever hear.

Image: Discogs

10. Steve Guttenberg briefly played Barbarino on television.

The commercial for the Up Your Nose With A Rubber Hose board game utilized look-alikes. While the Barbarino fill-in, sitting on the far right, is hardly shown, that is indeed future Police Academy star Steve Guttenberg.

11. Groucho Marx was supposed to appear in the episode "Sadie Hawkins Day."

Kaplan was a massive fan of Marx, and based the Sweathogs off the Marx Brothers dynamic. The comedy icon was invited to appear at the end of "Sadie Hawkins Day," yet when the actor, then in his mid-80s, showed up on set, he appeared too frail. It was decided to not show him in such a state. Even the behind-the-scenes photos were reportedly tossed to preserve Groucho's dignity.

Image: Wikimedia Commons