FOREST, Mississippi (AP) — The Mississippi man known as “Case 1,” the first person to be diagnosed with autism, has died.

Donald G Triplett was the subject of a book titled “In a Different Key,” a PBS documentary film, BBC news magazine installment and countless medical journal articles.

But to employees at the Bank of Forest, in a small city about 40 miles (64 kilometres) east of Jackson, he was simply “Don,” WLBT-TV reported.

Triplett died Thursday, confirmed Lesa Davis, the bank’s senior vice president. He was 89.

Triplett worked for 65 years at the bank where his father Beamon Triplett was a primary shareholder.

“Don was a remarkable individual,” CEO Allen Breland said of Triplett, who was known as a fiercely independent savant. “And he kept things interesting.”

Triplett, a 1958 graduate of Millsaps College, enjoyed golf and travel and was frequently flying to exotic locales, Breland said.

“He was in his own world, but if you gave him two, three-digit numbers, he could multiply them faster than you could get the answer on a calculator,” he told the television station.

Triplett’s autism diagnosis arose from a detailed 22-page letter sent to a Johns Hopkins researcher in Baltimore containing telling observations by his parents about his aptitudes and behaviour. The letter remains a primary reference document for those who study the disorder.

Oliver Triplett, Triplett’s nephew, told The Times-Picayune/The New Orleans Advocate that his uncle’s story offers hope to parents of children who are different.

“They can see Don and a community who embraced him,” he said. “As a whole, Forest encouraged him and accepted him. It gives people who have children on different levels of the spectrum hope that their children can live happy and full lives.”

Funeral services for Triplett will be at 11 am Monday at the Forest Presbyterian Church.