David Bradley Carter (born December 5, 1973) is an American film and television actor, guitarist, painter, sculptor, and photographer, known for playing Charlie Lange in True Detective and Leland Gruen in Sons of Anarchy.
After suffering from brain disease and tremors that caused his hands to shake, he underwent brain surgery in 2013, which he recorded and posted on YouTube. The video went viral, and he became known as the "guy playing guitar during brain surgery". (Via Wikipedia)