Watch Transformers One Trailer No. 2

Chris Hemsworth, Brian Tyree Henry, Scarlett Johansson, Keegan-Michael Key, Steve Buscemi, Laurence Fishburne, Jon Hamm and more star in 'Transformers One.' This installment is the untold origin story of Optimus Prime and Megatron. 'Transformers One' hits theaters on Sept. 20.