In the opening minutes of Liz Garbus’ new documentary, famed explorer and filmmaker Jacques-Yves Cousteau is shown talking to a group of young children. As he patiently answers their questions about his work and life under the ocean, they gaze at him in rapt wonder. Filmgoers, especially those of a certain age who grew up devouring his iconic television series The Undersea World of Jacques Cousteau, will feel exactly the same way while watching Becoming Cousteau, receiving its world premiere at the Telluride Film Festival.

Although his reputation has somewhat faded with time, it’s hard to overstate how revolutionary Cousteau’s film and television work was. Nowadays, you can’t channel surf for more than two minutes without encountering a beautifully photographed nature documentary. In 1956, however, when his Oscar- and Palme d’Or-winning feature doc The Silent World (co-directed by Louis Malle) became an unlikely commercial hit, there were very few films utilizing underwater photography.

Garbus’ documentary takes a deep dive (apologies for the pun) into Cousteau’s life and career, using copious amounts of archival video and audio footage, as well as excerpts from diary entries read by actor Vincent Cassel, to deliver an immersive, intimate biographical portrait. While clearly laudatory in detailing its subject’s impressive achievements, the film doesn’t shy away from addressing some problematic professional and personal aspects, including his early neglect of his parental responsibilities.

As a young man, Cousteau aspired to becoming a French Navy pilot, but his life changed when he was involved in a serious car accident at age 26 that left him with severe injuries. When he began swimming to help himself recuperate, he became fascinated by free diving and spearfishing. “It seemed like the act of a mythical demigod,” he says of the latter.

“I became an inventor by necessity,” Cousteau says. He created a waterproof housing for movie cameras so he could film underwater and co-invented a revolutionary breathing apparatus, the Aqua-Lung, in order to dive deeper and longer. In 1951, he converted a former British minesweeping boat into a research vessel dubbed Calypso, which became iconic via his films and television series, and inspired John Denver’s 1975 hit song.

Along the way he married Simone Melchior, who loved the sea as much as he did. Nicknamed “The Shepherdess,” she oversaw operations aboard the Calypso even while avoiding the media spotlight.

Cousteau disdained the term “documentary” for his cinematic efforts, referring to them instead as adventure films. Television producer David Wolper recognized the potential of his work, resulting in the hit television series The Undersea World of Jacques Cousteau, which ran on ABC from 1968 to 1976. When Cousteau began emphasizing environmental themes in a largely downbeat manner, the ratings suffered and the show was dropped, although he created a second series for PBS that ran for several more years.

The documentary chronicles Cousteau’s evolution from prospecting for petrochemical companies to finance his expeditions to becoming a staunch environmentalist, creating the Cousteau Society to spotlight the fragility of underwater ecosystems. He spearheaded efforts to protect Antarctica and was involved in the creation of the first Earth Summit, held in 1992. He’s shown posing for the event’s official photo, chatting and laughing alongside dozens of world leaders.

Garbus doesn’t shy away from dealing with Cousteau’s sometimes messy personal life. His obsessive dedication to his work kept him away from sons Philippe and Jean-Michel for long periods when they were young. Philippe later became instrumental in his father’s career but died in a plane crash when he was only 38. A severely depressed Cousteau declared, “I’m going to work to the bitter end. That’s my punishment.” Simone died of cancer in 1990, and six months later he married the much younger Francine Triplet, with whom he already had two children.

Becoming Cousteau succeeds beautifully in its goal of reminding viewers of Jacques Cousteau’s important legacy of underwater exploration and environmental activism. Consistently engrossing as well as informative, the film delivers a richly humanistic portrait of a complex, indefatigable figure who introduced multiple awestruck generations to the wonders beneath the sea.