Del Martin, the pioneering lesbian rights activist who was first to marry in San Francisco, died today at age 87. She leaves behind her partner of over fifty years, Phyllis Lyon.

The pair were married on June 16th, the first day that gay marriage was available in California, by Mayor Gavin Newsom. They were also the only couple to marry in San Francisco on that historic first day.

Martin and Lyon founded the Daughters of Bilitis in 1955, the first social and political organization for lesbians in the United States.

Martin died Wednesday morning at a San Francisco hospital, reports The Associated Press.

Gay groups mourned the loss of such a prominent activist.

“We are deeply saddened by the loss of Del Martin and our sympathies are with Phyllis Lyon in this difficult time,” said Truth Wins Out Executive Director Wayne Besen. “Through her bravery and persistence, Del gave people like myself the opportunity to live openly and honestly and I thank her for her enormous contributions to the GLBT community. She is a genuine hero and a person future generations will look up to with admiration and pride.”

Media watchdog group GLAAD called her “a leader and an inspiration.”

Pro-gay group Parents, Families and Friends of Lesbians and Gays (PFLAG) said Martin “lifted the hearts of Americans, again and again, as they [along with her partner] led the fight for marriage equality in California and the nation.”