Gustav Wagner was an Austrian Nazi SS officer and deputy commandant of the Sobibor extermination camp in German-occupied Poland during the Second World War. Known among prisoners as "The Beast of Sobibor," he became one of the most feared figures in the Nazi camp system, notorious for his cruelty and personal involvement in the murder of prisoners.

Before arriving at Sobibor in 1942, Wagner participated in the Nazi T4 euthanasia programme at Hartheim killing centre in Austria. At Sobibor, where approximately 250,000 Jews were murdered according to historical estimates cited in the documentary, he oversaw daily camp operations and terrorized prisoners through violence, humiliation, and executions.

Following the Sobibor prisoner uprising in October 1943, Wagner helped dismantle the camp and destroy evidence of Nazi crimes. After the war, he escaped to South America with the assistance of Nazi escape networks and lived in Brazil for decades. Despite his arrest in 1978 and extradition requests from several countries, Wagner never faced trial for his crimes. His life ended under controversial circumstances in October 1980.