Thunder Flash is an eighteen-year-old pegasus stallion who lives in Ponyville. He originally lived in Canterlot for a few years before moving to Ponyville. He currently works at the town's weather center.
Thunder Flash's past is one still clouded even to himself. He's unsure of where he came from, nor who his parents are. He's given up trying to remember where he came from, but since neither Celestia nor Luna has seen him before, he concludes he isn't from Equestria. During a flight accident in Canterlot, he lost a lot of blood from his injuries, and Luna's blood was the only compatible type with his, since he doesn't have family. Since then, about a quarter of his blood is alicorn, shown by his unusually large wing-span. He also attained some sort of ability to control the current of lightning around him, due to the magical properties of alicorns and pegasi. After a year of staying in Canterlot's hospital, and another year in Canterlot, he left for Ponyville after the remark from the Princesses that he was unsociable and caused a lot of trouble.
Originally quiet and conflicted with his inner emotions, he kept to himself and enjoyed causing trouble. He would constantly cause problems for other ponies, and was very selfish to his own ends. Most of this is due to his uncertainty about his past, having lost his memory after the accident. The Princesses themselves couldn't find any records of him at all. He had already attained his cutie mark before the accident, and he's unsure as to what it means.
After arriving in Ponyville, he fell in love with the mare Rainbow Dash, attracted by her gutsy attitude and her loyalty to her friends. Although he knows its a childish dream to chase after her, he nevertheless continues to watch her from afar. After meeting many of the random ponies in Ponyville, he's gotten very annoyed at them and has started developing a natural hate for randomness. But he's very caring, and can appear as a playboy the way in looks after mares. Which is true, since he acts cool sometimes. His hobby is sleeping and slacking off, and can usually be found napping in a tree or on a cloud.
His first major involvement in Ponyville was in a battle against a griffon known as Thal Siris. Both of them fought blade to blade in an aerial battle, after which Thal fled through a kind of portal. Directly after that incident, he was repairing the damage done to the town when he found Sora Dash flying in the air. The both of them introduced themselves to each other, after which Thunder Flash started training Sora in the art of using a sword. Sora however, uses a Keyblade, and in a practice battle revealed that Sora was as strong as Thunder. Both of them bonded quite well, Thunder Flash acting as a good big brother figure to Sora Dash.
Deciding to take up law, he nevertheless barely passes the bar exam to become a lawyer. He was given the position of a temporary defense attorney, a lawyer hired free of charge when no other lawyers are available for the defendant. Although he didn't do particularly well due to the lack of clients, he generated a form of attitude to investigate and ponder about even the slightest details.