Marshall is one of the villains of the 2007 psychological thriller, Mr. Brooks. He was played by William Hurt.
When Earl Brooks is compelled to kill again, Marshall gets more repetitive and once again operates as his vicious alter ego. Even though Brooks does try to resist his killer side and only Brooks can talk to and see Marshall. Marshall usually sucks Brooks into murder like killing a couple after years of trying to defy him. He and Brooks predict Smith pulling a gun on Brooks and thanks to Marshall's urging, Earl Brooks kills Smith.
He also implies that Brook's daughter is hiding something besides being pregnant and shows hatred towards Smith. At the end of the movie, Brooks still tries to fight him as he urges him.