As more people identify as non-binary, individuals often introduce themselves by the pronouns with which they identify. E-mails are signed with he/him/his, she/her/hers or they/them/theirs. Pronouns are now playing a prominent role in gender politics. This may seem new, but linguists have been puzzling over pronouns for a century or more. Conflicts over pronoun usage goes back to the days of suffrage and gender equality, today it's the usage of a word thought to be plural --"they"--to denote a gender-neutral singular person.
At one point, "they" was an acceptable word for a singular third person, but that changed over time. The search for the perfect gender-neutral singular pronoun goes back to the 19th Century, even words used today and considered neo-pronouns, ze, hir, and hirs, or thon goes back in some form to the 1800's. In his book on the search for an alternative to "they," Dennis Baron, a professor emeritus of English and linguistic at the University of Illinois, lists over 50 pages of alternatives proposed by linguists, language amateurs, and cranks, most of which never entered anyone's vocabulary. That history is related in "What's Your Pronoun? Beyond He & She."