Judy Heumann was refused a place in public school as a child because, in the words of the school, she was a "fire hazard." She was denied a teacher's license as an adult because officials decided she could not evacuate a classroom in an emergency. She used a wheelchair after surviving polio at eighteen months old, and she spent her life turning that kind of exclusion into a movement -- one whose crowning achievement was the Americans with Disabilities Act (ADA), the world's first comprehensive civil rights law for people with disabilities. Signed on July 26, 1990, and celebrated today as National Disability Independence Day, that law exists in large part because of one person: Judy Heumann, the woman often called the "mother of the disability rights movement." As she once observed, “when other people see you as a third-class citizen, the first thing you need is a belief in yourself and the knowledge that you have rights. The next thing you need is a group of friends to fight back with.” Pictured here as TIME's Women of the Year for 1977, Heumann was at the center of multiple battles for civil rights for people with disabilities, most famously the 504 Sit-In. Organized by Heumann, Kitty Cone, and Mary Jane Owen, over 150 other activists occupied the San Francisco Office of the U.S. Department of Health, Education and Welfare for 28 days in 1977 demanding the implementation of Section 504 of the Rehabilitation Act, one of the first federal disability rights laws. Equally importantly, Heumann helped change the narrative about disability, showing that the true burden of disabilities is how others respond to it: "Disability only becomes a tragedy when society fails to provide the things we need to lead our lives — job opportunities or barrier-free buildings, for example," she once said. "It is not a tragedy to me that I'm living in a wheelchair."