Casper is expressed in the second season by Robbie Sublett in the film , Matthew Géczy in the first season and Devon Werkheiser . Casper is voiced by Robbie Sublett in the film , Matthew Géczy in the first season and Devon Werkheiser in the second season . Casper is expressed in the film by Devon Werkheiser , in the first season of Robbie sublett and in the second season of Matthew Géczy .