Henry Havelock Ellis, known as Havelock Ellis (2 February 1859 - 8 July 1939), was a British physician and psychologist, writer, and social reformer who studied human sexuality. He was co-author of the first medical textbook in English on homosexuality in 1897, and also published works on a variety of sexual practices and inclinations, including transgender psychology. He is credited with introducing the notions of narcissism and autoeroticism, later adopted by psychoanalysis. He served as president of the Galton Institute and, like many intellectuals of his era, supported eugenics.
In November 1891, at the age of 32, and still a virgin, Ellis married the English writer and proponent of women's rights, Edith Lees. From the beginning, their marriage was unconventional, as Edith Lees was openly lesbian. At the end of the honeymoon, Ellis went back to his bachelor rooms in Paddington. She lived at Fellowship House. Their "open marriage" was the central subject in Ellis's autobiography, My Life.
According to Ellis in My Life, his friends were much amused at his being considered an expert on sex. Some knew that he suffered from impotence until the age of 60. He then discovered that he could become aroused by the sight of a woman urinating. Ellis named this "undinism". It is now more commonly called urolagnia. After his wife, Edith Lees, died, Ellis formed a relationship with Francoise Lafitte who was French. She found his desire for "undinism" charming and indulged it with him.