Comic book supervillain, owned and published by DC Comics. They made their first appearance in 1946 in Sensation Comics #59, written by William Moulton Marston and illustrated by Harry G. Peter.
Originally known as just the Snow Man, the character dressed in a blue robe with a blue mask and blue derby hat while using high technology to freeze a small farming community to extort money from the residents. After being defeated by Wonder Woman, the Snow Man is unmasked as a woman, Bryna Brilyant, who had adopted a male disguise to throw suspicion away from her true identity. (This gender-flipping "woman disguised as a man" trope was used fairly often by Marston, the kinkiest writer in comics.)
The character returned in 1948, renaming herself as the Blue Snowman. She kept the snowman mask and derby hat, but ditched the robe for a rotund metal bodysuit, so she looked more like an actual snowman. Her primary weapon was a large cannon that produced blue-colored snow that froze anything it touched. The derby also produced blue snow, and the pipe of the snowman suit actually fired icicles.
Once the Golden Age ended, Blue Snowman only rarely appeared in comics. One of her few Post-Crisis appearances was in an issue of the "Power Girl" series, where she was defeated by Power Girl and Dr. Mid-Nite. She was then unceremoniously eaten by a giant alien insect.
After another couple multiverse reboots, the new version of Bryna Brilyant was given the Blue Snowman powersuit by criminal mastermind Veronica Cale. After several defeats at Wonder Woman's hands, Brilyant revealed that they wore a masculine bodysuit because they were genderfluid.
The character is still very minor, not much better than D-list villainy, so they still appear very rarely in comics, and so far, their genderfluidity hasn't been mentioned very often, and not much interesting has been done with the idea yet.