Complex sentence: During the production of the film, the character model department was headed by Joe Grant, whose department was responsible for the building of three-dimensional clay models of the characters in the film, known as maquettes.
Split into simpler sentences: During the production of the film the character model department was set-up headed by Joe Grant. The character model department was responsible for the building of three-dimensional clay models of the characters in the film, known as maquettes.