John Rykener, also known as Eleanor, was a 14th-century gender-nonconforming male prostitute arrested in December 1394 for performing a sex act with John Britby, in London's Cheapside, while wearing female attire. Although historians tentatively link Rykener, who was male, to a prisoner of the same name, the only known facts of Rykener's life come from an interrogation made by the mayor of London. Rykener was questioned on two offences: prostitution and sodomy. Prostitutes were not usually arrested in London during this period, while sodomy was an offence against morality rather than common law and so pursued in ecclesiastical courts. There is no evidence that Rykener was prosecuted for either crime.

Rykener spoke of being introduced to sexual contact with men by Elizabeth Brouderer, a London embroideress who dressed Rykener as a woman and may have acted as procurer. According to the court transcription of this account, Rykener had sex with both men and women, including priests and nuns. Rykener spent part of summer 1394 in Oxford, working both as a prostitute and as an embroideress, and in Beaconsfield had a sexual relationship with a woman. Rykener returned to London via Burford in Oxfordshire, working there as a barmaid and continuing with sex work. On returning to London, Rykener had paid encounters near the Tower of London, just outside the city. Rykener was arrested with Britby one Sunday evening in women's clothes, and was still wearing them during the interrogation on 11 December. There, Rykener described prior sexual encounters in great detail. But it appears that no charges were ever brought against Rykener; or at least, no records have been found suggesting so. Nothing definite is known of Rykener after this interrogation; Jeremy Goldberg has tentatively identified a John Rykener imprisoned by and escaping from the Bishop of London in 1399 as the same person.

Historians of social, sexual and gender history are especially interested in Rykener's case because of what it reveals about medieval views on sex and gender. Goldberg, for example, views it firmly in the context of King Richard II's quarrel with the city of London—although he has also questioned the veracity of the entire record and posited that the case was merely a propaganda piece by city officials. Historian James A. Schultz has viewed the affair as being of greater significance to historians than more famous medieval stories such as Tristan and Iseult. Ruth Mazo Karras—who in the 1990s rediscovered the Rykener case in the City of London archives—sees it as illustrating the difficulties the law has in addressing things it cannot describe. Modern interest in John/Eleanor Rykener has not been confined to academia. Rykener has appeared as a character in at least one work of popular historical fiction, and the story has been adapted for the stage. Rykener's persistent use of women's clothing and presentation as an embroideress, prostitute, or barmaid has prompted some contemporary scholars to suggest that Rykener was a trans woman.

Prostitution was tightly regulated in fourteenth-century England, and brothels—although not prostitution itself—were illegal in the City of London. City authorities tended not to prosecute individual sex workers, but focused on arresting the pimps and procuresses who lived off them. Prostitution was perceived as most dangerous to the moral fabric of society. Another sexual offence for which people could be prosecuted was sodomy, but this would generally be by the church in its own courts. Of these two sexual offences, sodomy was deemed the worse. The thirteenth-century philosopher and theologian Thomas Aquinas compared prostitution to a sewer controlling the flow of waste, saying that if one were to remove it, one would "fill the palace with foulness". Aquinas then expanded on the point, saying "take away prostitutes from the world and you will fill it with sodomy". Prostitution was thus seen as a necessary evil that, if not eliminated, could be controlled. The Lord Mayor of London's secular court would not have been seen as competent to hear cases involving either offence.

In late-fourteenth-century London, it was considered socially unacceptable for a man to habitually wear women's clothes. There were exceptions if it was deliberately obvious or necessary—for example, in theatre, or mystery plays. Corpus Christi mystery plays, as the historian Katie Normington notes, provided an occasion "where gender identity could be tested or disrupted". Conversely, the limited number of such opportunities, says Vern Bullough, meant that male-to-female transvestism was effectively non-existent in public society. But beneath the surface, suggests Ruth Evans, London was "a place of unrivalled sexual and economic opportunities".

Hermaphroditism too had a legally recognised status; the thirteenth-century jurist Henry de Bracton, for example, had discussed it in his Laws and Customs of England, and there was a strong tradition of fictionalising it. The best-known, a story told by at least four separate German chroniclers in the 1380s, was from Lübeck. The protagonist dressed as a woman by night and sold sex out of a booth. By day, he was a priest and was eventually discovered when a client recognised him celebrating mass. The medieval historian Jeremy Goldberg has compared the Lübeck and Rykener cases: both involved "cross-dressing, dishonesty, the close association of priests with homosexual activity, and the eventual intervention of the city authorities".

All that is known of Rykener's life comes from the answers given during the interrogation in the Lord Mayor's court, following Rykener's arrest in December 1394. At these proceedings, Rykener described in some detail coming to learn the trades of prostitution and needlecraft when living with a London embroideress, also telling the court with whom and where Rykener subsequently plied those trades. According to the transcription of the proceedings, Rykener had only recently returned to London after visiting other parts of southern England prior to being arrested in Cheapside, a busy commercial district of London.

At the interrogation, Rykener described being first dressed as a woman at the Bishopsgate house of one Elizabeth Brouderer. Following the 1348–1349 outbreak of bubonic plague—which killed between one quarter and one half of the English population—female apprenticeships had become as common as those for boys, particularly in London. Here Rykener was taught how to sleep with men as a woman and to be paid for doing so, as well as embroidery, and may have completed an apprenticeship under Brouderer, as female apprentices did. Rykener described the situation in some detail: