Flash Sentry

A pegasus stallion, Ex-Royal Guard of Canterlot that occasionally served as a guard in the Crystal Empire before the faithful day he decided to volunteer for Twilight Sparkle's new 'Supersoldier' startup during her craze to make sure that Equestria was the most well defended and well protected land in the world. The temptation of being first of a new wave of super ponies, and the chance to be a little closer to her, sounded great on paper.
He probably should have looked at said paper before finding out the hard way it involved ripping out a lot of innards to turn him into a cyborg augmented to be stronger than any other pony.
After escaping, he swore revenge before he was taken over and reprogrammed mentally by Fawntaine and being forced to work for Blueblood, all with the intention to steal Twilight's schematics and turn Fawntaine into a technological powerhouse. He was forced to work with his fellow experiment in body augmentation, Fizzle, for some time before they messed up once too much, and had to go on the run.
Ending up on the doorstep of a certain bacon haired pony...