Ely's daughter, Kirsten, tells TMZ he passed away at home at the age of 86 peacefully surrounded by family on September 29th ... and went on to pay an emotional tribute to him in a lengthy IG post, remembering him as one of the greatest men to ever live -- and, a personal idol of hers.

She says her dad always brought a wave of positivity with him wherever he went ... saying his life story was one of relentless perseverance to do what was right, adding she's doing her best to walk in her father's footsteps.

Kirsten says she's comforted by the knowledge her father has been reunited with her mother, Valerie, and her brother Cameron.

Ron started acting professionally in the late 1950s ... but, it wasn't until 1966 when he got his big break -- playing the titular character on the "Tarzan" TV show across 57 episodes from 1966 to 1968.

His other credits include ... "Wonder Woman," "The Love Boat," "L.A. Law," "Doc Savage: The Man of Bronze," "The Friend Who Walked the West," and multiple other 'Tarzan' projects over the years. Ely wrote a pair of novels in his later years as well.

Ely's life was upended in 2019 when his son, Cameron -- reportedly suffering from the early stages of CTE -- stabbed his mother, Ron's wife, to death. Cameron was then shot and killed by Santa Barbra County sheriff's deputies.

Ron sued the department the following year ... claiming the deputies did not try to render medical aid as they should have after Valerie was stabbed and Cameron was shot.

Ron was 86. He's survived by Kirsten and his other daughter Kaitland.