Okay I'm here with the essay loosely inspired by this post and how the pronoun debate online always defaults to english which diminishes the work of people all over the world.
In swedish we have three singular third pronouns; han/honom (he/him), hon/henne (she/her) and den/det (it). Our language is thankfully not very gendered at all, which makes the whole thing a lot easier than for example latin based languages that genders exactly everything (we do basically have two neutrals instead, which is quite confusing at times, but I digress).
Back in the day when people wanted to convey an unknown or irrelevant gender they would say "han eller hon" meaning "he or she". It works but is quite cumbersome. In writing it was often "han/hon". This was the norm for as long as I know. Very similar to english.
I followed a few feminist blogs in the late 00s and they didn't like that "he" was always put first and started to write it as h*n, h/n, h#n and similar. It works in writing for an ingroup, but you can't pronounce that. So people settled for hen, a simple third option to hon and han.
It should be noted that at this point it was mostly still used for when the gender of a person is unknown or irrelevant, as the discussion around non binary people still hadn't reached the mainstream. Non binary people became almost an afterthought, as in "here's a gender neutral pronoun for when gender is irrelevant, or I guess if you're neither male or female".
So these feminist blogs started using hen, leftist debaters and writers for magazines and newspapers picked it up and started using it, which of course started a shit storm from the right. Newspapers had to figure out if they should allow it in their style guides or not.
People also started using it as a suffix where words usually ended in -en, like bloggen (the blog) to blogghen, klänningen (the dress) to klänninghen etc. It was mostly a joke around leftists to rile up the right and it sort of worked.
Nöjesguiden, a free weekly magazine about nightlife and culture, published a whole issue in february of 2012 where they changed the name to NöjesguideHen and every he and she was changed to the neutral Hen. The same year the children's book Kivi och monsterhund was published, only using hen.
Later that year, DN, one of the biggest daily newspapers in the country issued a statement saying that they would not allow hen as it could be seen as a political statement. People were talking more about the queer aspects of the word at this point which was apparently too much for DN.
This caused a bit of an uproar, lots of essays and blog posts and debates were had, and in 2014 SAOL, Word list of the Swedish Academy, added hen as a new word which was seen as the official stamp of approval for it, and publications started to follow suit.
Today it is used widely both in text and speech, it's a lot less loaded now as people just have gotten used to hearing it and it's actually quite practical. In hindsight it's fascinating that a massive culture debate that lasted for a couple of years now has completely calmed down and it became a new standard in the language in a relatively short amount of time.
TLDR; feminists and queers started to use a new neutral pronoun, the right had a breakdown, bon appetit.