Tommy Flanagan (born July 3, 1965) grew up in Glasgow, Scotland, in a "rough" section of the city.
One night a group of thugs attacked him as he left a pub, and tried to rob him. He attempted to fight back and was stabbed in the process, and from this came his facial scar; it's known as a Glasgow Grin.
He could have died, but he survived and chose to become an actor. He got his big break in the film Braveheart (1995) which starred Mel Gibson.