Who is Martin Seligman from the nonfiction book, Grit?

Martin Seligman, whom the author refers to as "Marty," is the author's graduate school advisor. Seligman developed the idea of Positive Psychology, and helped to develop the idea of learned helplessness. This is the idea that suffering that people feel that they cannot control (or that they cannot really control) leads to clinical depression. Seligman and a colleague named Aaron Beck developed the idea of learned optimism, or the ability to be resilient in the face of adversity.