Final answer:
Martin Seligman is the author of the learned helplessness model and the reformulated version of learned helplessness in psychology. He also co-authored a book on positive psychology.
Step-by-step explanation:
Martin Seligman is the author of several theories in the field of psychology. One of his notable theories is the learned helplessness model, which states that individuals who believe they have no control over negative life events may become helpless and prone to developing depression. Another theory associated with Seligman is the reformulated version of learned helplessness, which focuses on attributions made for negative life events and their contribution to depression. Seligman also co-authored a book titled 'Authentic Happiness: Using the New Positive Psychology to Realize Your Potential for Lasting Fulfillment', which explores positive psychology and ways to achieve happiness.