Non-binary badasses have been around forever. Thanks to my family's gift of Bygone Badass Broads, I got to learn about two transgender trailblazers that prove this point. Egypt's first female pharaoh, Hatshepsut, and Sweden's androgynous gyrl king, Christina.
What makes a person transgender or non-binary is simple. As a trans person myself (who writes fantasy), I define transgender as the transcendence of society's traditional definitions of gender. This is represented by someone who identifies, dresses, or behaves outside of the expectations of the man or woman box. Transgender is a huge umbrella term so there's really no one way to be trans.
In Hatshepsut and Christina's cases, these womxn took on power, roles, and expression traditionally reserved for men. Hence transcendence and my claiming of them for the transgender, non-binary team.
Beardless statue of Hatshepsut
Bearded statue of Hatshepsut