The Roman Emperor Elagabalus has often been characterised as transsexual. Cassius Dio has this to say about him:

When trying someone in court he really had more or less the appearance of a man, but everywhere else he showed affectations in his actions and in the quality of his voice.

For instance, he used to dance, not only in the orchestra, but also, in a way, even while walking, performing sacrifices, receiving salutations, or delivering a speech.

And finally, — to go back now to the story which I began, — he was bestowed in marriage and was termed wife, mistress, and queen. He worked with wool, sometimes wore a hair-net, and painted his eyes, daubing them with white lead and alkanet.

Once, indeed, he shaved his chin and held a festival to mark the event; but after that he had the hairs plucked out, so as to look more like a woman. And he often reclined while receiving the salutations of the senators.

The husband of this "woman" was Hierocles, a Carian slave, once the favourite of Gordius, from whom he had learned to drive a chariot.

He comments on Elegabalus' preferred form of address:

and then, when Aurelius addressed him with the usual salutation, "My Lord Emperor, Hail!" he [Elagabalus] bent his neck so as to assume a ravishing feminine pose, and turning his eyes upon him with a melting gaze, answered without any hesitation: "Call me not Lord, for I am a Lady."

As well as this tidbit:

He carried his lewdness to such a point that he asked the physicians to contrive a woman's vagina in his body by means of an incision, promising them large sums for doing so.

So, assuming Cassius Dio is telling us the whole truth here, Elagabalus made himself look like a woman, acted like a woman, had himself referred to as a woman, and wanted to physically become a woman. That definitely fits the idea of someone believing they are of the "wrong" sex.

Yaaaaaaaay! A question in my main field of interest (Psychology & Psychiatry);

So the first recognised person to undergo sexual reassignment surgery ("MTF" to be specific) was Danish artist, "Einar Wegener" (1882-1931) , here is what Einar looked like before transitioning

Whilst Wegener was male he was a successful painter who had a wife, Gerda Wegener (nee Gottlieb) who was also an artist. That's how Wegener met Gottlieb because they were both studying at Copenhagen's * Det Kongelige Danske Kunstakademi* ("Royal Danish Academy of Fine Arts") they married in 1904 when Wegener was 21 & Gottlieb was 19.

After leaving Art school both Wegeners' worked as illustrators, with Einar specialising in landscape paintings & Gerda specialising in illustrating for books & magazines (as well as the occasional erotic artwork). Gerda was famed for her paintings of beautiful women. see here. It wasn't uncommon for Gerda to paint women in sexual positions. see this painting [NSFW]

Because of Gerda's quite controversial artwork & the realisation that many of her paintings of women were actually Einar dressed as a lady.. This happened because one of Gottlieb's models was absent & so Einar had to fill in. Einar felt comfortable dressing as a women & so posed as one for Gottlieb's later paintings & dressed as a woman (going under the name "Lili/Lilly Elbe") in private.

Both of these reasons were big players in Einar & Gerda having to leave Copenhagen, they settled in Paris between 1912-1913 . Paris at the time was liberal enough for both to live. Whilst in Paris Elbe & Gottlieb introduced themselves as such, with Wegener's alterego (elbe) coming out more & more.

Gottlieb was fairly open & alright with the idea of Einar living as a Lili Elbe, mainly because whilst in Paris, Gottlieb experimented with Women as well as the fact that Elbe was introduced as Gottlieb's sister, so she was open to many orientations & gender identities.

Some say like "Nikolaj Pors" for instance that Gottlieb encouraged the "alterego" to come out:

Some nights when things were a little boring, Gerda would say, 'Let Lili come over tonight', and Einar would hop into women's clothes."

In 1930, Elbe went to Germany for surgery, which at the point was experimental. Elbe was under Magnus Hirschfeld, a gay Jewish sexologist who was a big advocate of sexual minorities. Elbe had a total of 4 surgeries over 2 years, the first one being an orchiectomy ("removal of testicles").

The further operations were under Kurt Warnekros, a gynaecologist, the next operation was to have a penectomy ("removal of the penis & scrotum"). To feel complete, Elbe wanted to have ovaries as well so that was the third operation. The fourth operation took place in 1931 & that was to create a vagina. However due to organ rejection, Elbe died three months later. Here is a picture of Lili Elbe after transitioning

there's also the disease (if it can really be called a disease, I don't really know how to call it) in which an individual's psychology tells them they belong in the gender opposite from their bodies, which totally justifies a gender swap,

This is known as "Gender Dysphoria", the criteria for being diagnosed is as follows:

For a person to be diagnosed with gender dysphoria, there must be a marked difference between the individual’s expressed/experienced gender and the gender others would assign him or her, and it must continue for at least six months. In children, the desire to be of the other gender must be present and verbalized. This condition causes clinically significant distress or impairment in social, occupational, or other important areas of functioning. Gender dysphoria is manifested in a variety of ways, including strong desires to be treated as the other gender or to be rid of one’s sex characteristics, or a strong conviction that one has feeling and reactions typical of the other gender.

Taken from the latest edition of the Diagnostic and Statistical Manual of Mental Disorders ("DSM"). The majority of transsexuals experience gender dysphoria.

Now that's the definition but to truly understand GD we also need to differentiate between the psychological definitions of Sex & Gender. Sex refers to;

a person’s biological status and is typically categorized as male, female, or intersex... There are a number of indicators of biological sex, including sex chromosomes, gonads, internal reproductive organs, and external genitalia.

Gender refers to;

the attitudes, feelings, and behaviors that a given culture associates with a person’s biological sex. Behavior that is compatible with cultural expectations is referred to as gender-normative; behaviors that are viewed as incompatible with these expectations constitute gender non-conformity.

Even if one doesn't identify as transsexual (e.g. Transman/Transwoman) they don't have to identify as male or female either, there are many different gender identities, a GI is defined as;

as a personal conception of oneself as male or female (or both or neither). This concept is intimately related to the concept of gender role, which is defined as the outward manifestations of personality that reflect the gender identity.

Some of the different gender identities include; Agender/Genderless, Bigender, Genderqueer, Gender Fluid & Two-Spirit.

Sources & Further Reading:

1. Niels Hoyer's Man into Woman: The First Sex Change

2. Dr. Rainer Herrn's Schnittmuster des Geschlechts: Transvestitismus und Transsexualität in der frühen Sexualwissenschaft ("Patterns of gender: Transvestism and transsexualism in the early sexology") a study which contains an account of the operations Elbe went through & Hirschfeld's involvement in them.

3. Sabine Meyer's Wie Lili zu einem richtigen Mädchen wurde': Lili Elbe: Zur Konstruktion von Geschlecht und Identität zwischen Medialisierung, Regulierung und Subjektivierung ("As Lili was a real girl ': Lili Elbe: For the construction of gender and identity between medialisation, regulation and subjectivation")

4. David Ebershoff's The Danish Girl, a slightly fictionalised account of the life of Lili Elbe. It has been adapted into a film of the same name to be released later this year. The trailer can be seen here

Just a couple previous answers that may interest you.

Could you please explain the topic of transgender in a historical sense?

Has there been any writing about Transgender people in the past? Or is it some type of newer phenomenon brought on by the availability of hormones?

How did transgender people get by in the Stone Age?

Tuesday Trivia | Crossdressing and other Alternate Expressions of Gender

AskHistorians AMA Thread: History of Sexuality

I've never heard of anyone in history that could actually be identified as a transsexual person before the 70's.

That's the easiest part to answer. The term was coined by Dr. Magnus Hirschfeld in the 1923. Adopted into English in the middle of the 20th century. And came to be defined as "person seeking some form of medically-assisted gender transition"--the technology for which didn't exist prior to the 20th cent.

Even in so narrow a sense (which would by definition preclude examples before 1920's) that's many decades of history prior to your 70's supposition.

Lili Elbe (1882-1931)--soon to be the subject of uber-Oscar-bait film "The Danish Girl"--just happens to be the first publicly identifiable person, by those criteria.

Moving backwards to the previous century, there are abundant well-documented examples of persons successfully (and secretly) living outside his/her assigned gender. Perhaps most notably Dr. James Barry (1795-1865). But given that most lived as male, an argument may be made that desire for greater independence/economic opportunity may have played some role in the choice.

This points-out the great difficulty with your question in ever more distant times. You don't want to know about gender-variant behaviors (something demonstrably, and unsurprisingly, existing across many cultures and eras). You want to know what the motivation for the behavior was. Specifically, if some historic individual's self-concept was sufficiently similar to an identity professed by people now.

What did people think is already the most difficult type of historical question. What did people think about themselves is a giant step further into the unknown.

First, the easy part to answer: there were certainly transsexuals (in the modern sense) before the 70’s. For example, Christine Jorgensen was the first transwoman to be widely known in the United States as having undergone sexual reassignment surgery, back in the 50’s, and there were some people medically transitioning decades before that.

As for earlier? Keep in mind that it’s a bit of a problem to apply contemporary Western notions of sexuality and gender identity to people of different times and cultures. As you mention, homosexual behavior has always been around, but the idea of someone being a gay person is relatively new. Likewise, there is a long history of gender variance and cross-gender dress and behavior across many cultures, and this includes the relatively modern concept of someone being a transgender person (having an internal sense of gender identity, distinct from sexuality, that differs from sex assigned at birth, and taking steps to live as that gender). I’m not sure how much the changing conception is due to a “culturally influenced aspect of human sexuality” and how much is the medical advances in surgeries and hormones and their accessibility. It was simply much harder to transition before these.

Still, we do have accounts of people prior to the twentieth century who lived as the opposite sex, with the important disclaimer that it’s really hard to tell what an individual’s motives were. It may have been for practical reasons (e.g. to pursue homosexual relationships or economic opportunity), for “gender identity,” or some combination or other reasons entirely. I happen to know more about female-to-male cases, so I can give you a few examples of those (given that they all lived as men for many years and never voluntarily switched back, I am going to use male pronouns):

• Dr James Barry was a British surgeon who lived as a man from 1805 until his death in 1865.

• Albert Cashier was a Union soldier in the Civil War who lived as a man from at least 1862 to 1913.

• Murray Hall was a New York politician who lived as a man from the 1860’s until his death in 1901.

• Charley Parkhurst was a stagecoach driver and rancher who lived as a man from the 1820’s until his death in 1879.

Back to the contemporary case: there are transgender people who (intentionally) do not particularly conform to traditional gender roles; see, for example, Lou Sullivan and his work to remove same-sex attraction as a barrier to access to medical transition. And it’s difficult to answer your question about the fantasy society where men and women are treated entirely the same (is everyone bisexual?) without getting too far into speculation. But at least in the US, recent increases in gender equality and in tolerance of sexuality/gender variance have not stopped people from identifying as transgender.

Edit: formatting

Thank you all for your excellent answers! You've all helped me to understand transsexuality a lot better! All hail r/AskHistorians!!!