JR Martinez burned his face when he was a soldier in the US military. He had a terrible accident while he was on duty.
Apparently he was driving his Humvee around Iraq when he bumped into a land mine and a big explosion set the car on fire.
The other guys in the vehicle were were thrown away by the explosion but JR Martinez got stuck below of the vehicle in the middle of the flames.
JR Martinez was eventually rescued but his skin got serious burns and he was treated a long time for them. I like how he looks now, his scars are a sign of how brave and how much of a survivor he is.
Here's a picture before and after his face got burned.