The Dark Wizard starts with a dream about falling.

Dean Potter, once one of the most famous climbers in the world, sits talking to the camera about the same recurring dream he's had since he was a child.

"When I was a little boy my first memory was this dream of falling," Potter says. "I always wondered as I got older, you know if it was some premonition of me falling to my death. But I just feel it so strongly — needing to go towards that unknown and that fear."

SEE ALSO: 25 best documentaries on Max to learn something new

The dream is mentioned again and again throughout Peter Mortimer and Nick Rosen's four-part HBO docuseries. It's both an inciting incident for Potter's obsession with pushing the envelope and part of the mystery surrounding his character.

The Dark Wizard does an engaging — and often highly stress-inducing — job of exploring this mystery, from Potter's childhood and rise in the climbing world to his persistent struggles with mental health, in unflinching detail.

What's The Dark Wizard about?

Credit: HBO

Over four episodes, the docuseries focuses on the life, achievements and complex personality of Dean Potter, a rock climber who branched out into — and often devised — a number of high-risk extreme sports. Roughly working through his life in chronological order, the series combines climbing footage, animated journal entries, and interviews with Potter's friends, contemporaries, rivals, and partner Jen Rapp, offering an insight into a man who seemed equal parts driven and haunted.

Potter's life, in short, revolved around risking it. We see him breaking the speed record for 3000-foot ascents of Yosemite's El Capitan, free soloing (climbing without a rope) various never-before-conquered routes in Yosemite, freeBASEing (a method pioneered by Potter in which he climbs ropeless while wearing a backup parachute) on the Eiger, walking barefoot across ropes strung between two high ledges, and proximity flying with a wingsuit (a form of BASE jumping which uses a modified suit to enable gliding through the air).

Potter's life, in short, revolved around risking it.

The documentary is filled with extreme sports, in other words, but to call it an extreme sports documentary would be doing it a disservice. As the title suggests, The Dark Wizard is really a portrait of the man at its centre — a humanising psychological study of a near mythic figure.

The Dark Wizard almost acts as a prequel to Free Solo

Given that free soloing in Yosemite was a big focus of Potter's, it's unsurprising that Alex Honnold — the climber famous for the first ever free solo ascent of El Capitan, who recently found additional fame soloing Tapei 101 live on Netflix — makes an appearance. What's more interesting is just how much of an impact the two clearly had on one another.

The rivalry between Potter and Honnold is unpacked in the documentary through Potter's friends and Honnold himself, who speaks with his familiar blunt honesty about how he systematically ticked off Potter's achievements in Yosemite before setting his sights on beating Potter's own personal lists of goals (his 2008 free solo of Half Dome being one of the most notable).

As well as being a tense insight into competition between two athletes at the top of their game, these sections of the docuseries serve to illustrate a key aspect of Potter's personality: the struggle between doing something for the love of it and his own ego.

Featured Video For You How 6 generations of iPhone captured 20 years of motherhood in 'Motherboard'

The Dark Wizard is an extremely stressful watch

Credit: HBO

The Dark Wizard does an impressive job of showing Potter's internal conflicts. He wants to do things for the art and spirituality, but his competitiveness leads to him taking bigger and bigger risks; he wants to live a free life without anyone controlling him, but he's also being offered sponsorship and large financial deals.

One particularly stress-inducing episode sees Potter travelling to China to complete a highline walk — balancing on a thin rope between two peaks — live on state media TV, for a payment of $200,000. The buildup is almost as hard to watch as the act itself. Potter argues with the people involved through his translator, demands that they don't use a safety net, and then repeatedly falls from the rope in practise runs leading up to the live broadcast. He crashes out at those closest to him and withdraws into himself completely. On the big day, when he somehow manages to make it across the line while millions of people watch, he breaks down on the far side.

This pattern — a tense buildup to a high-risk act that Potter feels pressured to complete — taps into the theme at the heart of The Dark Wizard: mental health.

The documentary is a powerful exploration of mental illness

It's clear from the series that Potter suffered with serious depression.

"It was always a struggle with his mind," Potter's friend Brad Lynch, who documented some of his most famous climbs, says early on in the first episode. "Even when I first met him he would get in his head. Like, really down. And there would be times that we'd sit together and have more than a few beers or whatever...we would literally just sit there and just cry. Like fucking weep. Both of us were just like, what is it that's stirring this shit in my head?"

Risking his life, the documentary suggests, is a kind of coping mechanism for Potter.

As Lynch is talking, we see Potter's journal entries come to life. "I need to quiet my mind," reads one. "Find clarity through emptiness."

Later, in one of the most important lines in the documentary, Lynch sums up what he believes Potter is doing whenever he takes extreme risks: "I started to realise his only therapy was the death consequence."

Risking his life, the documentary suggests, is a kind of coping mechanism for Potter.

"When I'm leashless, out on the line or on the rock, free solo, I need total concentration or I'll die," we hear him say in an old interview. "Somehow, when my life's on the line, it brings my senses to a heightened state of calmness and clarity. It's the most powerful feeling I've ever experienced."

This level of depth is what makes The Dark Wizard such a powerful series. Yes, there's breath-taking footage of the many awe-inspiring acts that made Potter famous. But rather than purely mythologising him, the filmmakers have gone to great lengths to give insight into his personal struggles and motivations. The end result is nerve-wracking, enthralling, and — in the documentary's final moments — almost unbearably sad.

The Dark Wizard premieres on HBO on April 14 at 9 p.m. ET, with new episodes airing weekly.