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Comet is the name of two fictional comic book characters owned by DC Comics whose adventures have been published by that same company. The first character was a sapient horse with magical powers who was once a centaur in ancient Greece. The second character is a shapeshifter with three forms (male, female, and winged centaur). Both characters are connected to the Superman family of titles.

A very different Comet was introduced in Supergirl #14 (October 1997). This version was originally introduced as a hero with flight and cold-generation powers. Comet's appearance was unclear, as when using his powers he was surrounded by an aura of cold that made him resemble an actual comet. Comet looked like a man with three fingers, horse-like legs, long white hair, and a star mark on his forehead. There was a lot of speculation about who Comet was, but it was revealed that Comet was Andrea Martinez, a gay stand-up comic, who like her friend Linda Danvers (who could turn into Supergirl), could shape-shift between her human and super-powered forms (however, Comet's change also involved changing gender, from the female Andrea to the male Comet).  Soon, it was learned that Comet's male form was originally Andrew Jones, a (male) jockey, who had been trampled by horses and "rebuilt" by an organization called "The Stable" as a superhuman with equine DNA. He rebelled against the organization and began operating as a superhero. On one of his first missions he attempted to save a despairing Andrea Martinez (who had just come out to her parents, and been rejected) from an avalanche, but they both died. As with Matrix and Linda Danvers (who had merged into Supergirl, the Angel of Fire), this caused them to combine into one being: the Earth Angel of Love. Comet originally was in love with Supergirl, and since he was the Angel of Love, made her have feelings for him too, but she rejected him when she learned he was also a woman. This opened the door for the third Angel, Blithe, the Angel of Light, to use her powers to exploit Comet's heartbreak, and turn them against Supergirl. She enabled Comet to fully embrace their angel powers, transforming him/herself into a winged centaur.  Blithe deceived Comet into joining forces with the Carnivore (a powerful demonic creature who despised the Earth Angels, and sought their power). The Carnivore lost control, however, when Andrea abandoned her anger, learning that her mother had died, and had left a video apology for her actions. The three Earth Angels worked together to stop the Carnivore. Comet began a relationship with Blithe, since she loved both their forms (revealing that Blithe is bisexual).
Comet (DC Comics)