James Gunn called on his Guardians of the Galaxy actor Bradley Cooper for a surprise Superman role because he needed someone who "could walk in the footsteps of Marlon Brando"

Superman is packed with surprises, but one of the biggest is Guardians of the Galaxy actor Bradley Cooper making an appearance as none other than Jor-El, AKA Clark Kent's biological father.

Jor-El was played by Marlon Brando in the Christopher Reeve movies, which, according to Superman director James Gunn, played a key part in Cooper's casting too.

"I needed somebody who could play Jor-El… who had the stature of what we imagine that character being," Gunn told Entertainment Tonight. "Somebody who could walk in the footsteps of Marlon Brando."

Cooper plays a slightly different version to Jor-El than we're used to, though. He appears as a hologram in the Fortress of Solitude as normal, but it turns out he sent his son to Earth with a pretty sinister message accompanying baby Clark, instructing him to conquer Earth.

"A lot of times, Jor-El is played by a 70 year old man, and that means he was 70 when he had a baby," Gunn added. "So I wanted somebody that wasn't too old… So I think that Bradley was perfect, he did it for me as a favor because he's my friend, and I really appreciate him doing it."

Luckily for Earth, Superman has no intention of fulfilling his father's ominous wishes, despite Lex Luthor's smear campaign against him.

In the new movie, Superman is played by David Corenswet, with Rachel Brosnahan as Lois Lane, and Nicholas Hoult as Lex Luthor.

You can catch Superman in theaters now. For more on the movie, check out our Superman review, or our guide to the Superman ending explained for a breakdown of the dramatic conclusion.