Legendary tennis commentator Bud Collins once wrote that no tennis player had ever overcome more obstacles to become a champion than Althea Gibson. This year, rightly, the U.S. Postal Service is marking the U.S. Open tournament with a first-class “Forever” stamp honoring the African-American tennis great from the 1950s.

Gibson, born in South Carolina in 1927 and raised in Harlem, won the women’s singles titles at Wimbledon and Forest Hills (at the U.S. National Championships, the forerunner of today’s U.S. Open) in 1957 and repeated both feats in 1958. She was the first black champion, male or female, at those tournaments. At a time when top tennis was remained an amateur sport largely played at private clubs that excluded blacks (and in many cases Jews as well), Gibson had to fight just to be allowed to play in the United States’ national championship at all.

But that realm of prejudice and privilege provided a paradoxical opportunity for Gibson. Gibson overcame the initial barrier to entry when she became the first African-American allowed to play at Forest Hills in 1950, and from that point on, she faced a pool of rivals that was limited by geography and wealth.

Tennis, whose most prestigious events were open only to amateurs (as they would be until the “Open” revolution of 1968), was the preserve of a close-knit community of the socially prominent and those able to attract their patronage. A disproportionate number of its top American players were from Southern California. The sport’s lack of professional opportunities—especially for women—discouraged participation by the athletically talented looking for a chance to cash in on their skill someday; Gibson herself even had a professional golf career in the absence of a similar women’s professional tennis tour at the time. Gibson, at 5’11”, was tall for a woman player at the time (and taller than many of the top women’s players even today), and her strength and athletic ability allowed her to overcome the poor quality of her initial instruction in the game. As the Postal Service puts it, Gibson “was fast, had a long reach, and relied on a booming serve and precise volleys,” as well as the determination necessary to win her first major championships at the age of 30.