Another answer is, "People with disabilities ... all of us, each of us ... represent ourselves." Others who care about us can help, and do their best to speak up for our needs and interests. But families, friends, doctors, teachers, and disability professionals can only do so much to speak for us. In the end, we need to speak for ourselves.
A more practical answer is that there are several disability organizations that in various ways do a pretty good job of speaking for what matters to Americans with disabilities of all kinds. Here are a few disability organization that are worth knowing about, especially now when politics and policy-making are in turmoil and hard-won progress is in doubt.
National Council on Independent Living (NCIL)
The national organization representing independent living centers all over the country. In addition to advocating for centers, NCIL has a strong voice in nationwide disability policy advocacy.
American Disabled for Attendant Programs Today (ADAPT)
The premier organizer of large-scale disability rights protests. ADAPT actions are legendary, but it also does smart, sophisticated policy analysis and traditional legislative advocacy. ADAPT is mainly focused on home care, while it's origins were in advocating for accessible public transportation.
American Association of People with Disabilities (AAPD)
A national organization aimed at encompassing the broadest range of disability issues and types of disability community.
Disability Rights Education and Defense Fund (DREDF)
This California-based organization focuses on defending disability rights in the courts, and development of sound policy. DREDF was instrumental in crafting the Americans with Disabilities Act.
Autistic Self Advocacy Network (ASAN)
Although ASAN focuses on autism issues, in particular advocating for more humane and autistic-person-centered approaches to autism, it has also become one of the most committed, razor-sharp advocates on the full range of disability issues.
ARCs haven't always been on the forefront of disability rights, and many chapters are still heavily invested in sheltered workshops and segregated programs. However, the national Arc organization has recently been a powerful, progressive voice on issues like health care and Social Security.
These are just a few national organizations. There are also organizations at the state level, and, of course, Centers for Independent Living in every state and territory ... all of which strive to amplify the voices of people with disabilities.