Henry Havelock Ellis, known as Havelock Ellis (2 February 1859 - 8 July 1939), was an English physician, writer, progressive intellectual and social reformer who studied human sexuality. He co-authored the first medical textbook in English on homosexuality in 1897, and also published works on a variety of sexual practices and inclinations, as well as on transgender psychology. He is credited with introducing the notions of narcissism and autoeroticism, later adopted by psychoanalysis. Ellis was among the pioneering investigators of psychedelic drugs and the author of one of the first written reports to the public about an experience with mescaline, which he conducted on himself in 1896.

Ellis was strongly opposed to the idea of castration for eugenic purposes. In 1909, regulations were introduced at the Cantonal Asylum in Bern, which allowed those deemed 'unfit' and with strong sexual inclinations to be mandatorily sterilized. In a particular instance, several men and women, including epileptics and pedophiles were castrated, some of whom voluntarily requested it. While the results were positive, in that none of the subjects were found guilty of any more sexual offences, Ellis remained staunchly opposed to the practice. His view on the origin of these inclinations was that sexual impulses do not reside in the sexual organs, but rather they persist in the brain. Moreover, he posited that the sexual glands provided an important source of internal secretions vital for the functioning of the organism, and thus their removal could greatly injure the patient.  However, already in his time, Ellis was witness to the rise of vasectomies and ligatures of the Fallopian tubes, which performed the same sterilization without removing the whole organ. In these cases, Ellis was much more favorable, yet still maintaining that "sterilization of the unfit, if it is to be a practical and humane measure commanding general approval, must be voluntary on the part of the person undergoing it, and never compulsory." His opposition to such a system was not only rooted in morality. Rather, Ellis also considered the practicality of the situation, hypothesizing that if an already mentally unfit man is forced to undergo sterilization, he would only become more ill-balanced, and would end up committing more anti-social acts.  Though Ellis was never at ease with the idea of forced sterilizations, he was willing to find ways to circumvent that restriction. His focus was on the social ends of eugenics, and as a means to it, Ellis was in no way against 'persuading' 'volunteers' to undergo sterilization by withdrawing Poor Relief from them. While he preferred to convince those he deemed unfit using education, Ellis supported coercion as a tool. Furthermore, he supported adding ideas about eugenics and birth control to the education system in order to restructure society, and to promote social hygiene. For Ellis, sterilization seemed to be the only eugenic instrument that could be used on the mentally unfit. In fact, in his publication The Sterilization of the Unfit, Ellis argued that even institutionalization could not guarantee the complete prevention of procreation between the unfit, and thus, "the burdens of society, to say nothing of the race, are being multiplied. It is not possible to view sterilization with enthusiasm when applied to any class of people...but what, I ask myself, is the practical alternative?"

did his theories influence anything?
Furthermore, he supported adding ideas about eugenics and birth control to the education system in order to restructure society, and to promote social hygiene.