Diamond Tiara is an Earth filly, daughter of Filthy and Spoiled Rich.
Diamond Tiara has pink fur, blue eyes, and a curly, purple-and-white striped mane and tail. She wears a diamond tiara on her head, and her cutie mark is also a diamond tiara.
For a long time, Diamond Tiara has been prone to verbal (and sometimes mild physical) bullying towards "blank flanks" (foals who haven't earned their cutie marks) but since Crusaders of the Lost Mark, she has felt remorse for her bullying and become a better pony. Since then, she's also been a good leader like Twilight.