On Jun. 17, 2023, the Mississippi man known as “Case 1,” the first person to be diagnosed with autism, died. Triplett worked for 65 years at the bank where his father Beamon Triplett was a primary shareholder.

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 kilometers) 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.

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 behavior. The letter remains a primary reference document for those who study the disorder.