Sylvester Stallone is lending his distinctive drawl to upcoming animated film Animal Crackers.

The Rocky and Rambo star has joined the voice cast of the movie, and Danny DeVito and Sir Ian McKellen have also signed up, reported The Wrap.

A picture of Sir Ian McKellen at a charity event
Sir Ian McKellen will also voice a character in the animated feature (Ben Hider/Invision)

Patrick Warburton, Gilbert Gottfried and Raven-Symone are also among those on board for the film, which follows a family who inherit a ramshackle circus and a strange box of Animal Crackers that changes the people who eat them into the animals they’ve munched on.

Scott Christian Sava, who co-wrote the script and will co-direct, said he was stunned that so many of his dream cast agreed to do the movie.

He said: “When I was writing Animal Crackers I had specific voices in my head. Certain characters I wrote with actors in mind. Horatio was always Sir Ian McKellen. Brock was totally Patrick Warburton. Bullet-Man could be no one else but Stallone!

“To find out that each and every one of these actors have agreed to come on board this film and bring these characters to life… I’m flipping out.”