Charles Gaines, the author whose 1970s book and documentary “Pumping Iron” helped popularize professional bodybuilding and introduce Arnold Schwarzenegger to a wider audience, has died. He was 84. Gaines’ death is reported by his daughter, Greta Gaines, who says he died on Tuesday but does not disclose a cause of death.

Across the accounts, “Pumping Iron” is described as a pivotal work in bringing bodybuilding into the mainstream. The documentary associated with the project also played a role in raising Schwarzenegger’s profile internationally. Multiple outlets note that Gaines helped launch Schwarzenegger’s bodybuilding career through the attention generated by the book and documentary.

Arnold Schwarzenegger confirms Gaines’ death through social media, describing him as someone who was always seeking new frontiers and crediting him with helping connect Gaines and Schwarzenegger, as well as bringing attention to the niche sport of bodybuilding. Deadline also adds that Schwarzenegger calls Gaines a lifelong friend, while noting Gaines was born in Jacksonville, Florida, on January 6.