Fritz was a scarred, misshapen laborer who worked for Doctor Henry Frankenstein in the late 1800s. Frankenstein had Fritz accompany him to graveyards where they exhumed dead bodies that Frankenstein used in his work. He even had Fritz scale the gallows pole, cutting down bodies of criminals who were recently hung. He then sent Fritz to Goldstadt Medical College to procure a healthy brain. Fritz broke into the lecture hall of Doctor Waldman after class to steal a brain, but after being startled by a moving shadow, he dropped the glass jar containing the healthy brain. With little recourse, Fritz had no choice but to steal the brain of a known criminal instead. He brought it back to Frankenstein's laboratory at an old watchtower on his family's estate, but neglected to tell Frankenstein about his faux pas.
Doctor Frankenstein used all of these body parts in his obsessive quest to create an artificial human being. He had Fritz aid him in maintaining his laboratory equipment and preparing materials for the final operation. Fritz witnessed the success of his master's work as his creation was dramatically brought to life through bolts of lightning channeled into his body. This creature became known as the Frankenstein Monster.
Fritz hated the creature and took great delight in tormenting him whenever he could. When the monster first emerged from his cellar room, he began lashing out, and it took the combined efforts of Frankenstein and his old teacher, Professor Waldman to restrain him. Fritz however, only brought the creature to renewed levels of fear and rage by waving a torch in his face. He delighted in the fact that the monster feared fire. On another instance, Fritz took his frustrations out on the monster by lashing at him with a whip.
The monster finally took his revenge on Fritz though, breaking free of his chains and murdering him in the cellar of the watchtower. Doctor Frankenstein found Fritz' body hanging from a noose in the chamber.
- Dwight Frye's performance of Fritz perpetuated the archetype of a sycophantic, hunchbacked assistant that has been used in dozens of horror films, usually attributed to a character named Igor. The first pastiche of Frye's character was Bela Lugosi's scheming character, Ygor (not Igor), who was a mishapen assistant, but actually suffered from a broken neck and was not a hunchback. Another send up to the character was a man named Daniel, who was a hunchback, who worked for scientist Gustav Niemann in House of Frankenstein. This role also typecast Dwight Frye to playing roles involving the local town lunatic. Prior to Frankenstein, Frye also played the role of Renfield, the fly-eating madman who accompanied the vampire Dracula on his various ventures.
- Fritz is the first credited character seen in the film Frankenstein and the second character with speaking lines.
- House of Frankenstein presents the antagonist Gustav Niemann, who claims that his brother was Doctor Frankenstein's original assistant. This would suggest that Fritz's surname is Niemann as well. There is an incongruity with this notion however, as Niemann claimed that he learned about Frankenstein's experiments from his brother, even though Fritz died long before he would have had the chance to record his history or communicate with family members.
- In the original shooting script for Frankenstein (dated August 12th), Fritz was an unnamed hunchbacked, mute, dwarf. Also in this version, it was Frankenstein, not the assistant, who tormented the monster with matches and a whip. These details were switched to Fritz in the final draft in order to make Henry Frankenstein a more sympathetic character.
- The nature of Fritz' injury is undetermined. He is seen walking with a limp, but in the graveyard scene in the beginning of the film, he's holding his cane in his left hand. Later at the Watchtower, he is holding his cane in his right hand.
- In one of the early Watchtower scenes, Fritz stops halfway up the steps to pull up his socks before continuing on to fetch Doctor Frankenstein.
- Henry Frankenstein's son, Wolf von Frankenstein, blamed Fritz for the reason why his father's creation became a savage killer.