Fritz was the hunchbacked assistant to Dr. Henry Frankenstein. He helped dig up graves and snatch bodies in order to harvest body parts to construct a full viable human. However, he botched his solo assignment to retrieve a brain. As he was stealing it from a university, lightning startled him and he dropped it, destroying it. He instead grabbed the other brain that was corrupt.
When Frankenstein's Monster is brought to life, Dr. Frankenstein knows immediately the experiment is a failure and chains him up. Fritz wastes no time teasing the Monster with a torch, knowing the Monster is afraid of fire.
Eventually Fritz got too close and was murdered by The Monster.