Background: 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.
Context: Comet the Super-Horse is a fictional character that appears in comic books published by DC Comics. Comet was introduced in the Superboy story in Adventure Comics #293 in February 1962, then appeared regularly with Supergirl beginning in Action Comics #292 in September 1962.  Comet was one of a series of super-powered animals, including Streaky the Supercat and Beppo the Supermonkey, that were popular in DC's comics of the 1960s. Comet was Supergirl's pet horse and, while in his human form as Bill Starr, her brief boyfriend. Comet also had a brief romance with Lois Lane in her comic book.  As he described to her telepathically, he was originally a centaur in ancient Greece named Biron. The witch Circe gave him a potion to turn him fully human after he prevented an evil sorcerer poisoning her water, but by mistake made him fully horse instead due to the Sorcerer. Unable to reverse the spell, she instead gave him superpowers, including immortality. The Sorcerer asked his teacher to help him against Biron and they were able to imprison him on an asteroid in the constellation of Sagittarius, which he had been born under. However, when Supergirl's rocket passed, it broke the force field, enabling him to escape. Later, after meeting Supergirl, he went on a mission with her to the planet Zerox, where a magic spell was cast that turned him into a human, but only while a comet passes through the solar system he is in. As a human, he adopted the identity of "Bronco" Bill Starr, a rodeo trick-rider, whom Supergirl fell in love with.  Comet made sporadic appearances in comic stories through the 1960s, and even became a member of the Legion of Super-Pets, a group consisting of the aforementioned super-powered animals.  A traditional equine Comet is partially seen in Legion of Three Worlds #1. He is part of a display in the museum Superboy-Prime visits. The museum does have displays of the supermen of the multiverse and the Kristen Wells Superwoman so it is unclear whether this means Comet has returned to regular continuity.
Question: why did he change?
Answer: The witch Circe gave him a potion to turn him fully human after he prevented an evil sorcerer poisoning her water,

Background: Matthew Staton Bomer (born October 11, 1977) is an American actor, producer and director. He made his television debut with Guiding Light in 2001, and gained recognition with his recurring role in the NBC television series Chuck. He played the lead role of con-artist and thief Neal Caffrey in the USA Network series White Collar from 2009 to 2014. Bomer won a Golden Globe Award and received a Primetime Emmy Award nomination for his supporting role as Felix Turner, opposite Mark Ruffalo, in the HBO television film The Normal Heart (2014).
Context: Matthew Staton Bomer was born on October 11, 1977 in Webster Groves, Missouri, to Elizabeth Macy (nee Staton) and John O'Neill Bomer IV, a Dallas Cowboys draft pick. His father, John Bomer, played for the Dallas Cowboys from 1972 to 1974. He has a sister Megan Bomer and a brother Neill Bomer, who is an engineer. Bomer credits his own parents for being understanding when they sensed their young child was a little different from other kids. "I've always had an active imagination," says Bomer. He is a distant cousin to American singer Justin Timberlake, with whom he starred in the movie In Time in 2011. Timberlake and Bomer share common descent from Edward Bomer, who was born in 1690. Bomer's ancestry includes English, as well as Welsh, Scots-Irish, Scottish, Irish, Swiss-German, and German.  In 1995, at age 17, Bomer made his professional stage debut as Young Collector in a production of Tennessee Williams A Streetcar Named Desire (1947) staged by Alley Theatre, a company in the Downtown, Houston, at the Texas. A few years later he returned to the stage in 1998 in a re-presentation of the play Joseph and the Amazing Technicolor Dreamcoat by Andrew Lloyd Webber and Tim Rice in the play he lived Issachar - who was represented at the Utah Shakespeare Festival in Cedar City, Utah. Speaking about his first role in a production, Bomer said:  I started acting professionally when I was 17. I quit the team and did a production of A Streetcar Named Desire at the Alley Theatre in Houston. I used to drive down at the end of the school day, do the show, do my homework during intermission and drive an hour back to Spring to go to school the next day.  He grew up in Spring, Texas, a suburb of Houston, and attended its Klein High School in 1996, where he was a classmate of future actor Lee Pace and actress Lynn Collins. Pace and Bomer both acted at Houston's Alley Theatre, a non-profit theatre company. Bomer was nurtured throughout middle school by a theater arts teacher who taught him to improvise and give life to the characters he had created in his mind. His senior year, Bomer received a scholarship for some of his monologue performances, which led to his acceptance at Carnegie Mellon University in Pittsburgh, Pennsylvania. Where he graduated in 2001, with a Bachelor of Fine Arts degree, along with his friend and also actor Joe Manganiello.
Question: When was he born?
Answer:
October 11, 1977