Karl Dürrge (also known as Maria Dorothea Derrier: 1780–1835) was a Prussian intersex man, who had been designated on birth documents as female. After discovering the presence of ambiguous external genitalia, Dürrge assumed a male identity and made a living as a medical specimen. Dürrge's life provides insight into the way that persons with intersex variations were treated under the Prussian Code, which allowed such individuals to choose either male or female sex when they came of age. Together with reports of other intersex persons, who allowed their bodies to be used for medical research, Dürrge's case led to the establishment of guidelines for determining sex. Carrying their medical records with them, these intersex individuals helped develop the exchange of medical knowledge between ph