Many of the gags seen on the show were on-the-spot improvisations by Robin Williams, and later by Williams and Jonathan Winters. The improvisations proved so effective and popular that the series' writers soon included specific sections in the scripts where Williams was allowed to perform freely, marked as "Robin goes off here." If you pay attention to Pam Dawber, you can often see her having difficulty not laughing at the ad libs.
After the tragic death of Robin Williams, co-star Conrad Janis stated that Robin was "intelligent," and "had a photographic memory." He also said that he was "bright, happy, fun, high-spirited," and was "sweet, considerate, lovely, and courteous to everyone."
The show was an immediate ratings hit, finishing number three overall during its first season. For the second season, ABC moved the show's time slot to Sunday in an attempt to counter program CBS's Sunday comedy programming (notably Archie Bunker's Place). Almost immediately ratings took a sharp decline, and even after returning to the show's original Thursday Night time slot midway through season two, ratings never fully recovered.
Mork's Nanu Nanu hand gesture greetings was inspired by Spock's Live Long And Prosper hand salute from Star Trek. Plus, Mork's Orkan space suit had earlier been a costume from Star Trek: The Savage Curtain (1969) episode, and Robin Williams was a big fan of Star Trek.
Pam Dawber did not personally audition for the role of Mindy. To sell the show to the network, producer, Garry Marshall edited clips together of Dawber's performance from a failed ABC series of "Sister Terri," with existing footage of Robin Williams', two earlier guest-appearances as Mork on Happy Days (1974), of Happy Days: My Favorite Orkan (1978) & Happy Days: Mork Returns (1979). ABC was sold on the idea and the show was picked up. Dawber learned she had been cast in the series via industry trade paper, "Variety." It came to Pam Dawber as an expected surprise.
The name of Mork's Orkan Superior, Orson (they have a five minute conversation, before the closing credits begin) was chosen as a tribute to Orson Welles and his historic 1938 CBS Radio broadcast of H.G. Welles' "War of the Worlds", which was adapted for the American audience. Orson Welles chose to portray the Martians as landing in New Jersey.
Jonathan Winters' first appearance on the show was as Dave McConnell (one of Mindy's relatives) in "Mork and the Family Reunion". Winters went on to join the cast full-time as Mearth in the following season.
Mork & Mindy: Mork Meets Robin Williams (1981) was suggested to Garry Marshall, after Robin Williams specifically requested it, which allowed Robin Williams to be himself and so viewers could get to know the real Robin Williams and Mork learning about the nature of fame on Earth. Two months prior to the broadcast, John Lennon was assassinated by a deranged fan and is mentioned by Mork as one of the celebrities whose lives had been destroyed by the pressures of fame, when Mork makes his weekly report to Orson, as each episode is nearing its conclusion, just before Closing Credits begin.
Fred and Cora were written out at the start of the second season as it was felt the two didn't fit well into the show's younger demographics. The move was unpopular with viewers, and Fred and Cora were both brought back by the third season.
When Conrad Janis and Elizabeth Kerr temporarily left the show, their absences were explained by having Fred fulfilling his dream of becoming a conductor and going on the road and Cora joining him there.
Robin Williams has said he started using cocaine on the set of Mork and Mindy because he didn't know what to say in between takes to all the set people and all the celebrities hanging around watching the production. This would snowball into a cocaine addiction that would plague him for much of his life.
Producer Garry Marshall said he came up with the basic concept of the show during a phone call with an ABC executive. He said he set the show in the college town of Boulder because he had a friend with a child attending Colorado University.