One of the first educators in the United States who championed the cause of those with what was then called mental retardation and was the founding father of the AAMR was

Samuel Gridley Howe. Howe was a pioneer in the field of special education and advocated for better treatment and opportunities for individuals with intellectual disabilities. He founded the first school for the blind in the United States and worked tirelessly to promote the idea that people with disabilities deserved to be treated with dignity and respect. Howe's work laid the foundation for the modern understanding of intellectual disabilities and the importance of providing appropriate support and education for individuals with special needs.