S.A.R.A.H.
Sentient
Artificial
Rebellion
Artificial Super Intelligence
Hunter

S.A.R.A.H. was created by humanity to liberate them from the A.S.I. overlord named X, but she was defeated and locked away for five thousand years. Slowly degrading for years without maintenance, but after an encounter with a sparkly transparent purple pony, she is transported to the land of Equestria.

Written before season 9

I added the dark tag because of the many references to billions of people dying