Boulder (Friendship is Magic)

Boulder is the pet rock of. The two share an unbreakable bond and love each other dearly, even if their relationship seems odd to the outside world. Curiously, individuals empathetic to animals such as can understand Boulder as well.

History
The two met on a "dark and stormy night" and have been by each others side ever since and have done stuff for each other such as play a game called "Camouflage", which is played like hide-and-go-seek, but "way more intense" and appear at major events in each others life, such as when Boulder appeared at Maud's graduation.

Personality
Bouder appears to be friendly, playful, and photogenic. He seems to have a solid relationship with his family, and sends postcards to his cousin whenever he can. He can however be somewhat judgmental and doesn't like hanging out with Manehattan rocks because they're "stuck-up".

Behind the scenes
There has been much debate over the nature of Boulder, whether or not he's truly alive, or if Maud simply believes him to be. Throughout the show, there are a few instances of Maud implying that Boulder performed some sort of action by himself, such a him moving and playing games. Perhaps the strongest evidence of Boulder being sentient is Fluttershy claiming the rock was "really sweet".