Donald Triplett, the first person to ever be diagnosed with autism, passed away Thursday at the age of 89.

Triplett was diagnosed as a child by Johns Hopkins psychiatrist Leo Kanner. Triplett, who was known as "Case 1", had an excellent memory and ability to recite music, but was socially withdrawn and had food aversions.

Kanner began seeing Triplett in 1938, when he was 5 years old. Triplett was featured heavily in Kenner's 1943 paper, "Autistic Disturbances of Affective Contact."

Triplett worked at Bank of Forest, where his father Beamon was a primary shareholder, for 65 years. A Mississippi native, he graduated from Millsaps College in 1958.

11-YEAR-OLD AUTISTIC PIANO PRODIGY GOES VIRAL AFTER $15,000 SURPRISE GIFT FROM TEACHER

courtesy In a Different Key - Donald

Donald Triplett was the first person ever diagnosed with autism. (Courtesy In A Different Key)

"Don was a remarkable individual," CEO Allen Breland told WLBT. "And he kept things interesting."

Triplett was also a savant with unusual mathematical skills. He was extensively studied in publications ranging from medical journals to a book called "In a Different Key".

"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," Breland explained.

IS PARKINSON'S DISEASE, 'WORLD'S FASTEST-GROWING BRAIN DISEASE,’ MOSTLY PREVENTABLE? STUDY OFFERS CLUES

Donald G. Triplett

This image provided by WLBV-TV shows Donald Triplett, the Mississippi man known worldwide as "Case 1," the first person to be diagnosed with autism. Triplett died Thursday, June 15, 2023. He was 89. (AP Photo/WLBV-TV)

Triplett's special interests included golf and travel, and he frequently visited "exotic locales", according to Breland.

Triplett's nephew Oliver told The Times-Picayune/The New Orleans Advocate that his uncle's legacy gives hope to parents of autistic children.

"They can see Don and a community who embraced him," Oliver explained. "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."

CLICK TO GET THE FOX NEWS APP

The Associated Press contributed to this report.