As a young man, Flanagan was attacked by a gang in Glasgow, and stabbed in the face several times. Several commentators have pointed out they tried to give him a “Glasgow smile”.
He started working as a theatrical actor, but his big break came during Braveheart, where he was cast as an extra. Mel Gibson saw him and immediately gave him a much more prominent role in the film, because he felt the scars added realism to his character.
Thereafter Flanagan has appeared in several big-budget films, including Gladiator.
Now he is much older than this picture and wears a beard, which hides his scars quite effectively.