The Danish Girl Trivia

Brain Snacks: Tasty Tidbits of Knowledge

Einar Wegener is based on a real person, and although the novel is fiction, many of its elements are true. His wife painted pictures of him as Lili (and many of the paintings were erotic in nature.) The couple did live in Oscar Wilde's apartment. However, after Lili's death, Gerda (Greta in the novel) slipped into a deep depression. Lili Elbe's memoir, Man Into Woman, was published as a pulp novel in the 1950s, when her transition was treated as lurid and transgressive.
(Source. Warning: some explicit art is included on this page.)

At the library in Paris, Einar briefly reads the myth of Hermes and Aphrodite (17.1). Their child, Hermaphroditos, is where the word "hermaphrodite" originates. Hermaphroditos was depicted as having female breasts and male genitalia, so we can understand why Einar may identify with this mythical figure. He's like the myth brought to life.
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Some people believe that the real-life Einar Wegener had Klinefelter Syndrome, a genetic condition in which someone has two X chromosomes and a Y chromosome. The syndrome causes the person to have a feminine body and lower levels of body hair, like Einar. Could be true, but Lili Klinefelter doesn't have the same elegant ring to it that Lili Elbe has.
(Source.)