Chris Hemsworth made a highly-anticipated return to San Diego Comic-Con to promote 'Transformers One,' a new animated prequel to the Transformers franchise. The film, directed by Josh Cooley, explores the origins of Optimus Prime (Hemsworth) and Megatron (Brian Tyree Henry) when they were still friends known as Orion Pax and D-16. Co-stars including Keegan-Michael Key, Scarlett Johansson, Laurence Fishburne, Jon Hamm, and Steve Buscemi contribute to the ensemble cast. The presentation included a new trailer and three extended clips, highlighting Cybertron's society and the friendship-turned-rivalry between Orion and D-16. Initial reactions to the film praise its emotional depth, animation quality, and nostalgic charm. 'Transformers One' is set to be released in theaters on September 20.