One of the leading wildlife biologists of the 20th century, the American zoologist George Schaller has fought to save the world’s endangered creatures for over 50 years. Author of the seminal book, “The Mountain Gorilla: Ecology and Behavior,” which illuminated the life of gorillas in the wild and served as a basis for the work of Dian Fossey, Schaller won The National Book Award for his book, “The Serengeti Lion: A Study of Predator-Prey Relations,” in 1973 and the World Wildlife Fund Gold Medal in 1980. One man’s passionate fight to save our world is captured in Nature’s Greatest Defender, a film about Schaller’s unwavering dedication to the incredible wildlife that we must continually struggle to protect. He returns to the sites of some of his iconic studies to see what has happened to some of these extraordinary animals and their habitats. Narrated by Glenn Close. Directed by Cathe Neukum. Produced by Tom Veltre and Cathe Neukum.