Mason Haynes -- a longtime celebrity bodyguard who protected members of the Kardashian family and several other A-listers -- is dead.

A GoFundMe created for his family says Mason died in a traffic accident on July 4, just two days before what would have been his 53rd birthday.

Mason spent years working in close protection ... with the Kardashians among his first celebrity clients. He previously said he had worked with Kim Kardashian, Kris Jenner and Kanye West ... along with Kevin Hart, Nicki Minaj, Charlie Puth and Formula 1 star Lewis Hamilton.

He was also part of the family's security team when Kim was robbed at gunpoint in Paris in 2016 -- though he later declined to discuss the incident in detail.

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Mason's employer, Trojan Security UK, remembered him as an "absolute legend" in the close-protection industry ... sharing a photo of him working alongside Kris and saying he was gone too soon.

The fundraiser paints Mason as much more than muscle, describing him as a protector, mentor and prankster who made everyone feel like family. Organizers say hundreds of messages have poured in from people whose lives he touched.

Mason leaves behind his wife, Fay, daughter Brooke and son Noah. The fundraiser will help cover his memorial and ease the family's financial burden as they grieve.

He was 52.

RIP