The first use of the "cis" prefix referring to gender comes from a 1914 text by German physician and sexologist Ernst Burchard. He used "Cisvestitismus" to describe the inclination to wear clothing which conforms with a person's gender - the opposite of "Transvestitismus" (transvestism), the inclination to wear gender non-conforming clothes.
Burchard was a colleague of sexologist Magnus Hirschfeld, founder of the Institut für Sexualwissenschaft (Institute of Sexology). Hirschfeld and Burchard, as well as researching sexology and gender, worked together in activism for gay rights in Germany.
Both men sought to repeal Paragraph 175, a homophobic law which made sex between men a crime. They also co-authored research on sexology.