Diamond Tiara (voiced by Chantal Strand as a filly and Janeane Garofalo as a grown up) was a snobby, conceited school-age Earth pony and a minor antagonist who first appears in Call of the Cutie. She and Silver Spoon are classmates of the Cutie Mark Crusaders. She bullies them, along with her friend, Silver Spoon, and calls and picks on other ponies without cutie marks, "Blank Flanks". She is also the daughter of Filthy Rich, a successfull businessman who is friends with Granny Smith and the owner of his own company, Rich's Barnyard Bargains. Due to her cruel behavior, she is usally punished by him, for example in the ending of the "MLP: FIM" episode "Family Appreciation Day", being forced to wear a pair of bunny ears and hop around watering cans while singing the Alphabet song.
In Call of the Cutie, Diamond Tiara and Silver Spoon invite Apple Bloom and Twist to their cute-ceañera, a party for those who have recently earned their cutie marks. (The name is a pun on the Spanish quinceanera, a girl's "sweet 16" or coming-of-age party.) It's heavily clear that they were only invited so that other party attendees can mock them for their lack of marks. Twist manages to gain her cutie mark after finding her talent (making candy), but unfortunately, Apple Bloom doesn't earn hers before the party.
At the party, Apple Bloom tries to hide her lack of cutie mark with a table cloth, but bumps into Diamond Tiara and Silver Spoon. She claims that she got her cutie mark earlier, but doesn't want to show off and take attention away from the party's guests of honor. Diamond Tiara replies that she didn't want to see Bloom's cutie mark anyway. As Apple Bloom prepares to leave, she trips over the long table cloth and hits her head on the table that a radio was stationed on, thus exposing her flank. Diamond Tiara and Silver Spoon see that it's blank and don't hesitate to make fun of Apple Bloom, who is soon joined by two other blank flanks, Scootaloo and Sweetie Belle. The teasing gets ignored as Twilight Sparkle and Applejack explain that being a blank flank means still having many possibilities open. Diamond Tiara is later seen standing alongside Silver Spoon in the stairway, watching the other ponies play party games.
She appears again along with Silver Spoon on stage at the talent show in The Show Stoppers, as well as during the lesson in The Return of Harmony Part 1 and in The Cutie Pox with Diamond Tiara trying to prove in the school yard that Apple Bloom's cutie mark is a fake. Later she asks Cheerilee if it's really fake and is seen being jealous of Apple Bloom's loopty-hooping ability.
She appears in Family Appreciation Day, alongside her father, Filthy Rich. When she visits the farm with her father, she points out Granny Smith's odd behavior to Apple Bloom and convinces her of how humiliating it would be if Granny Smith spoke to her class. After Granny Smith impresses Apple Bloom's class with her presentation of how she helped found Ponyville when she discovered and learned how to cultivate zap apples, Diamond Tiara openly denigrates her. At the end of the episode, her father, evidently mad that his daughter insulted his most valuable produce supplier for his business, forces her to participate in singing to the water cans, much to her
frustration. In Hearts and Hooves Day is given a card from Alula to her surprise and then is seen checking her hooves and then reacts to Cheerilee.
In Hearts and Hooves Day, she is given a card from Alula, to her surprise.
In her next appearance in Ponyville Confidential, she is the chief in charge of the school paper: the Foal Free Press. She appoints the Cutie Mark Crusaders the writers of the gossip column to try to revived Diamond Tiara. When the Cutie Mark Crusaders attempt to resign their position, Diamond Tiara blackmails them with embarrassing photos. Diamond Tiara is later stripped of her position by Cheerilee, who gives it to Featherweight. In the end of the episode she has been demoted to take care of the printing press and the previous holder of that position, Shady Daze becomes the photographer and decides to take a picture of the demoted Diamond Tiara. The flash from the camera dazes her and makes her stumble upon the printing press, making her dirty with ink. As everyone is laughing at Diamond Tiara, the episode closes with her looking bitterly at the audience.
In One Bad Apple, she and Silver Spoon mock the Cutie Mark Crusaders float for the Summer Harvest Parade. When they notice Babs Seed, they point out her blank flank and ask her if she will join the CMC. Babs responds by the calling the CMC "crybabies" and destroying their float, to Diamond Tiara and Silver Spoon's delight. Babs joins them in bullying the CMC, until they save her from a sabotaged float. As Babs is about to leave Ponyville, Diamond Tiara bemoans her and Silver Spoon being left with the "blank flanks", causing Babs to turn on them, threatening to tell their mothers about their bad attitudes. In fear, Diamond Tiara and Silver Spoon back up and fall into a mud puddle, with Diamond Tiara's tiara ending up on the head of a pig.
In Flight to the Finish, she and Silver Spoon compete for the honor of being the flag bearers of the Equestria Games. They spy on the Cutie Mark Crusader's rehearsal, and realize that the trio might actually win. They then decide to undermine Scootaloo's confidence by mocking her inability to fly. In the end, Scootaloo and her fellow Cutie Mark Crusaders perform their act, winning the right to be flag bearers, to Diamond Tiara's displeasure.
- Diamond Tiara along with Silver Spoon are the only two villains to be seen in all 4 seasons.
- They are also the most recurring villains in the show.
- Ironically, Diamond Tiara's voice actress Chantal Strand has previously voiced two notable characters who are the polar opposite: Cassie on Dragon Tales and Bijou on Hamtaro.