Matriarch of the Apple clan and spunky old gal. You whippersnappers mind yer manners!
Granny Smith lives at Sweet Apple Acres, and is the grandmother of Applejack, Big McIntosh, and Applebloom. She is quite an elderly pony and until her recent surgery at the Hayo Clinic in Manehattan had a bad hip, forcing her to use a walker to get around most of the time. She is somewhat hard of hearing and doesn't always quite have a complete grasp on what's going on around her, but she is sweet-natured and friendly -- if a little prone to panic when confronted with loud noises or unexpected surprises.
As revealed in "Family Appreciation Day," Granny Smith was instrumental in the founding of Ponyville, thanks to her discovery of ZapApples and the peculiar arcane process of producing ZapApple jam. It's not clear exactly how long ago this was, but it is entirely possible that Granny Smith is even older than she looks.
Granny Smith's skill at baking (especially pies) is legendary. She is also a kind and well-loved babysitter.