Donald Gray Triplett, the first person diagnosed with autism symptoms, died Thursday, according to his longtime employer. Triplett was 89.

Triplett started working at the Bank of Forest in 1958 and was remembered as a "fixture" at the small Mississippi city bank that sits about 40 miles east of Jackson.

"Every employee that has come through our doors since then, has fond stories and memories of him that we will treasure -- looking enviously at his travel photos, having your picture taken by him as a new employee, a collection of trinkets & post cards given through the years, a nickname or number given when he met you, or even being shot by a rubber band," the Bank of Forest said in a statement on Facebook.

"Don was a fixture at the bank for almost 65 years, and he will remain a fixture in our hearts for years to come."

Triplett was identified as "Donald T." in the 1943 paper "Autistic Disturbances of Affective Contact" by Leo Kanner of Johns Hopkins Hospital and the subject of a PBS documentary film as well as the book "In a Different Key: The Story of Autism."

The book, written by John Donvan and Caren Zucker, was a New York Times bestseller and a finalist for the Pulitzer Prize in 2017.

Autism or autism spectrum disorder (ASD) incorporates a group of neurodevelopmental disorders causing impaired communication skills and social skills. ASD generally starts before three years of age and lasts a lifetime, but early intervention plays a role in treatment and progress.

There is no definitive medical test to diagnose autism. Instead, the disorder is diagnosed by observing a child's development.

Triplett was first examined by Kanner, a child psychiatrist, in 1938 and later becomes the first person diagnosed with autism symptoms. Kanner's paper elaborated on the idea that autism is related to a lack of parental warmth; this is later dubbed the "refrigerator mother" theory.

"Seeing his story unfold over the years has been an honor," the Mississippi bank noted in the statement.

"We are truly blessed to be a small part of his story as Autism's first child. Our thoughts and prayers go out to Don's family and his many friends. We ask that you keep our bank family in your prayers as well."

Funeral services for Triplett will be held on Monday in Forest, according to his obituary.