For director Damien Chazelle, there was only one choice for who he wanted to play Neil Armstrong in First Man.

While visiting the PEOPLE and EW video suite at the Toronto International Film Festival, Chazelle explained the project had been in the works with star Ryan Gosling for awhile. “Ryan and I started talking about this movie a while ago,” he said. “Back before we even made La La Land together. In my mind, I never really thought of anyone but Ryan in this role.”

Finding the right fit for Janet, Armstrong’s wife, was trickier, but Chazelle said once he heard Claire Foy (The Crown) read from a real interview Janet had once given, he was sold.

To help him prepare, Gosling turned to Armstrong’s sons and many others involved in the moon landing and his life. “Neil’s sons were very involved,” Gosling said. “A lot of people helping to add perspective and help us get to the man behind the myth. Neil and Janet and his family lived an extraordinary life.”

Chazelle reminisces about words of wisdom Gosling once shared that get to the heart of the film and the challenge of portraying Armstrong: “You think it’s a movie about someone who lands on the moon, but really it’s a movie about someone struggling to land on earth.”

Watch the clip above for more. First Man hits theaters Oct. 12.