Ursula K. Le Guin
On the planet Gethen, all inhabitants are "ambisexual". This means that they are all men and women at the same time. There is no gender in Gethen and, consequently, there is also no sexism. The biological manifestation occurs only in the procreation periods, when everyone can choose the sex they will assume. Unlike all inhabitants, the protagonist Genly has a defined gender and can mate at any time. In the context of Gethen, this makes him an aberration.
In general, it is this plot of The Left Hand of Darkness, published in 1969 and considered the masterpiece of the writer Ursula K. Le Guin. Now 87, the writer was the first woman to win the biggest awards in science fiction (Hugo and Nebula). The vast North American work brings together 21 novels, 12 books of poetry, 13 children's titles, as well as collections of short stories, reviews and scripts.