The Furer features as himself in ‘Herrliche Zeiten’, which features Charlie Chaplin, also appearing as himself. Charlie Chaplin’s final acting role was a cameo in ‘A Countess From Hong Kong, which he also directed, which starred Marlon Brando, who also starred in Apocolypse now, which featured Harrison Ford as, fittingly, Colonel Lucas.
This probably isn't all that hard, but I'm interested to see: John Lennon.