Aaayyyy! Happy Days, one of the biggest hit sitcoms in television history, has reached its milestone 50th birthday. Debuting on this day in 1974, ABC was in search of a replacement for the low-rated comedy The New Temperature’s Rising and the competition leading off Tuesday was steep: All in the Family spinoff Maude on CBS and crime solver Adam-12 on NBC. Given the success of the nostalgic theatrical American Graffiti (complete with the clean cut Ronnie Howard in the cast), the solution was simple: the tale of a high school student named Richie Cunningham, his family and his friends set in Milwaukee, Wisconsin in the the 1950s.

The original concept of Happy Days was introduced on ABC’s romantic anthology Love, American Style in a segment called Love and the Television Set. Specifically, a family in the 1950s, the Cunninghams, gets their first television and the neighbors are stirring with anticipation. Teenage son Richie (Ron Howard) and his friend Warren “Potsie” Weber (Anson Williams) assume it can be used as a chick magnet.

Here there was no Arthur “Fonzie” Fonzarelli or Ralph Malph, and the characters of Howard Cunningham and his daughter Joanie were played by Harold Gould and Susan Neher, respectively.

Gould was set to continue in the role, but when production of Happy Days was delayed he went abroad to perform in a play. Midway through the that play’s run, he decided to honor his commitment to the stage production and passed on Happy Days. That led to Tom Bosley being cast. Erin Moran, meanwhile, now played Joanie and Gavan O’Herlihy replaced Ric Carrott as the Cunningham’s older son, Chuck.

In what began as a nostalgic look at this middle class family and friends in the 1950s, filmed in single camera style, Happy Days finished season one as ABC’s second-highest rated series (behind The Six Million Dollar Man). Its overall ranking was No. 16 and the eventual breakout star, Henry Winkler as “Fonzie,” was not even in the opening credits.

Season two opened with Randolph Roberts taking over the role of Chuck, who vanished without a trace midway through the sophomore episodes, and Henry Winkler and Donny Most (Ralph Malph) were upgraded to opening credit status. In one particular season two episode of Happy Days (“Fonzie Gets Married”), the single camera format was dropped and three cameras with a studio audience was filmed as a test run. After falling out of the Top 30 that season, the decision was made to shift the focus to Winkler’s “Fonzie” and now film permanently with three cameras and an audience, which gave these later seasons a markedly different style. A hit was belatedly born!

In season three, Happy Days inched up to No. 11 overall for the season, and the first spin-off, Laverne & Shirley, starring Penny Marshall and Cindy Williams, was born. By season four, in 1976-77, Happy Days rose to the top-rated series in all of primetime and Laverne & Shirley was No. 2.

What do you do when a comedy and its spin-off hold the top two spots in primetime? You find another character to lead a series and along came Robin Williams as the zany Mork from planet Ork in two episodes of Happy Days. Flash to the 1977-78 TV season and the inaugural season of Mork & Mindy, starring Williams and Pam Dawber, tied Happy Days for third overall. First was Laverne & Shirley (with the non-related sitcom Three’s Company holding the No. 3 spot).

There was even talk of giving Henry Winkler his own show, but Winkler was satisfied where he was and Happy Days ended up enjoying a memorable 11 season run on ABC.

Of note in season five was the addition of Scott Baio as Fonzie’s cousin Charles “Chachi” Arcola. And, in the animation department in the early 1980s, came The Fonz and the Happy Days Gang, Laverne & Shirley in the Army and, ultimately, The Mork & Mindy/Laverne & Shirley/Fonz Hour.

Like any series, original stars began to exit and the ratings began to decrease on Happy Days. Ron Howard and Donny Most called it quits after season seven, which resulted in the additions of Ted McGinley as Cunningham cousin Roger Phillips and Cathy Silvers as the often talked about but never before seen Jenny Piccolo in season eight. Other cast additions included Lynda Goodfriend as Richie’s girlfriend (and eventual wife) Lori Beth, who was upgraded to opening credit status in season eight, and Linda Purl as Ashley Pfister, Fonzie’s love interest, and the late Heather O’Rourke as her daughter Heather in season 10.

When Erin Moran and Scott Baio (not to mention Al Molinaro as “Arnold’s” owner Al Delvecchio) exited for the ill-fated spin-off Joanie Loves Chachi, Crystal Bernard was added as Howard’s niece K.C.

After the cancellation of Joanie Loves Chachi in season two, Bernard was out and back were the romantic pair, who in the series finale (on May 10, 1984) tied the knot in the Cunningham’s back yard.

In honor of the 50 year mark, here are 10 fun factoids about Happy Days.

1) Prior to Happy Days, Ron Howard was known as young Opie Taylor on comedy The Andy Griffith Show. But in between the two shows he appeared in the two season drama The Smith Family, opposite Henry Fonda, in the 1971-72 TV season.

2) Erin Moran was only 13 years old when Happy Days began, but it was not her first regularly scheduled TV series. In 1968, at age eight, she was added to the fourth season of the family adventure drama, Daktari.

3) Henry Winkler skyrocketed to fame as Arthur “Fonzie” Fonzarelli, but a bigger name of note at the time was also up for the role: Mickey Dolenz of The Monkees.

4) Marion Ross credits her late friend, Bewitched star Sandra Gould, with helping her get the role of Marion Cunningham on Happy Days. Marion was invited to a dinner hosted by Gould and a casting person from Happy Days also was in attendance. Not long after the dinner Marion got a call from the studio.

5) Roz Kelly as daredevil cyclist Pinky Tuscadero was intended as a serious love interest for Winkler’s Fonzie. But after the three episode fourth season-opener, Kelly was quietly written off the series when she did not fit in with the rest of the cast.

6) Kelly reprised her Pinky role on the first episode of yet another Happy Days spin-off, Blansky’s Beauties. Although Nancy Walker as Nancy Blansky was introduced as Howard Cunningham’s cousin, Blanksy’s Beauties was set in the present (which at the time was 1977).

7) Eddie Mekka appeared as Joey DeLuca on Blansky’s Beauties at the same time he was playing Joey’s cousin, Carmine Ragusa (aka “The Big Ragu”) on Laverne & Shirley. Call it a time warp!

8) In the often debated is it a spin-0ff or not, ABC introduced a short-lived sitcom in September 1979 called Out of the Blue. The series starred Jimmy Brogan as Random, an angel-in-training who is assigned to live with (and act as guardian angel for) a suburban Chicago family (led by a single mom played by Dixie Carter), as well as work as a high school teacher.

Its status as a spin-off is in question because the first episode of Out of the Blue actually aired before its lead character, Random (Jimmy Brogan), made an appearance on Happy Days. But it did feature a crossover with Mork & Mindy before being canned after only eight episodes aired.

9) The fifth season episode of Happy Days titled “Hollywood” (part three) is where the phrase “jump the shark” originated. Henry Winkler’s Fonzie, as you might recall, responds a challenge to his bravery by wearing swim trunks and his trademark leather jacket, and jumping over a confined shark. The phrase was coined in 1985 by radio personality Jon Hein as a descriptor when a TV series begins to spiral downward. But Happy Days actually lasted for another six seasons.

10) Following the finale of Happy Days, five unaired episodes were burned off that summer. In the actual last episode, “Fonzie’s Spots,” Howard’s position as the Grand Poobah at the Leopard Lodge is threatened when he realizes he hasn’t recruited any new members in the past five years. That leads Fonzie, Roger, and Chachi to volunteer to join.

Given the ultra cool Fonzie was seen in a pink and white rabbit contest, this true “jump the shark” moment was indeed the right time for Happy Days to call it quits.

Fifty years later, we remember and celebrate Happy Days as a major presence on television with, no doubt, one of the most iconic characters to ever hit the small screen. Happy half century mark!