Baker was born on June 2, 1951, in Chanute, Kansas. He grew up in Parsons, Kansas, where his grandmother owned a women's clothing store. His father was a judge and his mother was a teacher. Baker served in the United States Army from 1970 to 1972. He was stationed in San Francisco. After his honorable discharge from the military, he taught himself to sew. He used his skill to create banners for anti-war protest marches. It was during this time that he met and became friends with Harvey Milk. He also joined the group Sisters of Perpetual Indulgence stating "at first it was glamorous and political, but when the Sisters became more organized, I became a tool of the right wing and raised money for Jerry Falwell", referring to video and images of the group used for right-wing Christian efforts, "so I stopped."
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In 2003, to commemorate the Rainbow Flag’s 25th anniversary, Baker created a Rainbow Flag that stretched from the Gulf of Mexico to the Atlantic Ocean in Key West. After the commemoration, he sent sections of this flag to more than 100 cities around the world. Due to his creation of the rainbow flag, Baker often used the drag queen name "Busty Ross". Baker died in his sleep on March 31, 2017, as reported by the New York City medical examiner's office, at the age of 65, at his residence in New York City. The office's spokeswoman Julie Bolcer stated in an email that it was determined that the cause of death was hypertensive and cardiovascular disease. Upon Baker's death, California state senator Scott Wiener. In Baker's memory, NewFest and NYC Pride partnered with a design team to create ‘Gilbert’, a rainbow font inspired by the Rainbow Flag.