The character of Princess Celestia was originally supposed to be Queen Celestia, but Hasbro executives decided against the title of Queen since Disney had started the trend of animated Queens always being villains (excluding Elsa from Frozen). There later was an evil queen in the Season 2 finale (Queen Chrysalis) and possibly to build on that trend, the following season opened with an evil king (King Sombra).
Applejack is the only main character to remain mostly the same to the character she was based on. The other five main pony characters are all amalgamations of several characters from past generations of the show.
Andrea Libman does Fluttershy's singing voice, but not Pinkie Pie's. She stated the reason is because Pinkie Pie's high pitched voice tends to be a strain and that singing with it really hurts her throat.
Lauren Faust originally wanted to call the villain Nightmare Moon; Discord. But executives from Hasbro decided the name would be too confusing for their target demographic to comprehend. However when pitching for the second season premiere, Hasbro execs had no problem with the name when Executive Producer Lauren Faust mentioned the character was akin to Q from Star Trek: The Next Generation (1987) The comparison led to show producers actively seeking out John de Lancie to voice the character.
Because of the show's overwhelming popularity, which generates a high volume of fan-related content, the show creators have to do their research to make sure any one of the several pre-existing characters they wish to feature in an episode don't use a name that in any way sounds similar to one created by the fan base.
One regular background character pony with a hourglass cutie mark was noted by fans to have a distinctive resemblance to David Tennant's version of The Doctor of the British TV series, Doctor Who (2005). As such, he has taken on the fan nickname, Doctor Whooves, and is the subject of numerous fan creations, although his official name in the series is Time Turner. However, Hasbro has released an official figure of the character under the name Dr. Whooves with a collar and tie to accentuate the resemblance to the 10th Doctor. In addition, he appears in at least one variant cover of the official My Little Pony comic book with numerous references to the British series.
Producer Lauren Faust developed this series with the goal of creating a more sophisticated version of the My Little Pony franchise with more realistic and proactive characters than the usual sexist stereotypes she saw in earlier incarnations. For instance, the insistence on the part of Hasbro executives that clothes and fashion be a part of the characters' interest was addressed by making Rarity obsessed with fashion in the context of being a professional artist and a small business owner with clothes as her preferred medium.
Broke My Little Pony 'n Friends (1986) record of being the longest running My Little Pony TV series. Furthermore, at 100+ episodes, this series is also the longest running individual television series featuring a Hasbro toy property in the company's history.
Rainbow Dash is the only main character to feature a "cutie mark" that is a single symbol. Rarity, Applejack, Fluttershy, and Pinkie Pie all have "cutie marks" that are displayed in a cluster of three. Twilight Sparkle has a huge sparkle surrounded by five little sparkles.
Lauren Faust has said that she always felt that the Cutie Mark Crusaders - Apple Bloom, Scootaloo and Sweetie Belle - should have their own spin-off show aimed at preschoolers - where children learn how to do various activities as the three ponies try them out looking for their Cutie Marks.
While the show is labled for younger female audiences many of the jokes and references in the show have adult themes to them. Some include references to alcohol, movies for adults (like The Big Lebowski), and a few references to older bands and music (like Diamond Dogs).
Pinkie Pie's original design was a white Pegasus named and based on Gen 1 pony Surprise, but due to Hasbro no longer having the trademark they changed her to Gen 3 Pinkie Pie colors and name. Later it was decided to move her wings over to Posey-based Fluttershy. Some early show bible images used old concept art for Suprise in Pinkie Pie's colors to represent her.
Princess Luna's name was originally going to be Selena (presumably after the Greek Goddess of the moon, of which Luna is the Roman equivalent). Although her name was changed to legal reasons, she is still referred to as Princess Selena in a novelization of the first episodes.
Initial toys for Princess Celestia showed her with a pink coat, rather than white as is in the show. This is apparently due to Hasbro thinking a pink toy would sell better to young girls. Since a canon pink princess character - Cadance - was introduced, toys of Celestia have been released in show-accurate white.
Minor recurring villain Trixie was originally planned to be a boy, until the episode's scriptwriter suggested to Lauren Faust to make the character female. Faust later said that the change was absolutely for the better.
The fan favorite pony, a light grey pegasus mare, with blonde hair and a bunch of bubbles as her cutie mark, has many names. The fan name is Derpy, or Derpy Hooves, but that name was used in the show once, but some people found that name offensive (but derp/derpy means clumsy), so her show name is Ditzy Doo. But, on merchandise, her cutie mark is either a picture of a muffin, her face, or "Bubbles".
Fans still wonder about Twilight Sparkle's cutie mark. She is the only character with this unique, odd, cutie mark. All other ponies (and zebra), have cutie marks of either one symbol or a group of 3 symbols. Applejack has 3 apples. Rainbow Dash has one "speed" symbol. Twilight Sparkle's cutie mark appears to be a symbol, with 5 stars surrounding it.
Instead of using words like "God" or "Jesus" in common phrases people use, the characters in the show say "Celestia" instead. Princess Celestia is a bit like a god in the show (uses her magic to control the Sun and daytime, and has been ruling Equestria for over 1000 years). So it supposedly is more fitting to say that in the show instead.