Maud is Pinkie's older sister, who is very knowledgeable about geology. She grew up on the rock farm and is getting her "rocktorate" (like doctorate) in Rock Science. While she has a deadpan voice and sense of humor, she is not without emotions. She cares for Pinkie Pie, demonstrating this by rescuing her from a rock slide and hugging her when she was safe. She also has kept all the rock candy necklaces that Pinkie has traded her over the years, stating that she doesn't really like candy, but she does love Pinkie Pie. She also gave back the rock pouch that Pinkie gave her, after finding out she had paid for it by giving away her party canon. After getting the canon back (in exchange for the pouch), she explained to Pinkie that gift-giving isn't a competition of who can give better presents; it's an expression of love.
She has a pet rock named Boulder.
She always wears a blue frock, which obscures her Cutie Mark, which is a diamond. She likes to write both verse and free-verse poetry about rocks.
In Season 7 she graduated Vale-Rock-Torian of her class and got her Rocktorate. Then she moved to Ponyville (adjacent).
In Season 8 she got a boyfriend named Mudbriar, whom Pinkie Pie didn't get along with at first.
The Gift of the Maud Pie
Rock Solid Friendship
The Maud Couple