Fritz is a villain in the 1931 film version of Frankenstein. He is a hunchback who assists Henry Frankenstein in his experiments with life and death, even helping him collect pieces of corpses to assemble into what eventually became the Frankenstein Monster, a body Frankenstein created and gave life to.
When Dr. Frankenstein ordered him to steal a brain from the Goldstadt Medical School for use in the Monster, Fritz was startled by a noise and dropped the normal brain he was supposed to steal, and picked up a criminal's brain which was on the same table (this may have been due to illiteracy.).
This blunder is possible cause the homicidal acts the Monster would later commit. After the Monster's creation, Fritz developed an unexplained hatred towards him, possibly out of anger and frustration toward the world that mistreated the hunchback, although that is only a theory. He is often shown tormenting the Monster, including beating him with a whip and waving a lit torch in his face. This torture undermined Frankenstein's tries to train the Monster and make him more human. The Monster finally had more than he could stand and killed Fritz, hanging him from the ceiling in the dungeon where the Monster was being kept.