Complex sentence: Bermejo's incarnation of Joker in the graphic novel is similar to that of the design in "The Dark Knight" film due to him doing the same design as a gift for a Batman film site prior to the movie co-opting the design.
Split into simpler sentences: Bermejo's incarnation of Joker in the graphic novel is similar to that of the design in "The Dark Knight" film. Bermejo did the same design as a gift for a Batman film site prior to the movie co-opting the design.