On the day he would close the biggest deal of his life, Ryan Kavanaugh watched the sun rise from the 29th-floor conference room of one of Manhattan's most prestigious law firms.

It had been a long, anxious night at Paul, Weiss, Rifkind, Wharton & Garrison. As a wet snow began to fall outside, Kavanaugh, two lawyers, and a banker entered their 22nd straight hour negotiating the pact that would mark Wall Street's richest investment ever in Hollywood. Empty Dasani water bottles, crumpled M&M's wrappers, and thousands of pages of discarded drafts littered the huge, blond-lacquered conference table where the four men faced one another. They were reading the latest version of the deal, aptly nicknamed Mulholland Drive, after the most famously twisted street in Los Angeles.

This was the kind of high-stakes poker game at which Kavanaugh excelled. Even his enemies gave him that. In three years, he had helped funnel more than $3 billion of hedge fund, private equity, and bank money into the movie business. This deal would mean as much as $1.2 billion more for a potential avalanche of 45 films—if Kavanaugh could reel it in.

Red-haired and impish, the 32-year-old wore jeans, a wrinkled white dress shirt, and a pair of navy Converse sneakers. During lulls when documents were being printed, Kavanaugh played Blackhawk Striker, a computer game that he'd somehow figured out how to display on the room's 13-foot screen.

Every clause in Mulholland Drive—and there were hundreds of them—had to be vetted by three parties: Citigroup, Sony Pictures, and Kavanaugh's company, Relativity Media. That made for a complex, triangular dance executed by more than a dozen people—some in the room, others in adjoining offices, and a few on the phone from their homes in Los Angeles, where it was still the middle of the night.

After five months of negotiations, most of the issues left were the sort of what-if clauses common in such deals—convoluted hypotheticals that spelled out who'd do what for whom if things didn't work out as planned.

At every impasse, Kavanaugh practiced emergency shuttle diplomacy. First he'd retreat to an office dubbed the Sony Room, where he'd sit alone, phone in hand, relaying Citigroup's concerns to the studio's lawyers in California. Next he'd head down the hall to a second office, where two young, bleary-eyed Relativity executives crunched numbers on their laptops. Then he'd circle back to the conference room, where Citigroup's lawyer waited with Alfred Griffin, a director of Citigroup's markets-and-banking unit. Even at 7 a.m., Griffin was still wearing his dark-blue suit jacket, his red patterned tie perfectly knotted.

With everyone, Kavanaugh played the role of confidant. "I don't want you to be unhappy," he soothed them. "I don't want you to close the deal just to close it. I want you to be happy."

Then, around noon, an argument about certain funding guarantees that had been simmering for hours suddenly boiled over. It was a deal killer.

Kavanaugh quickly grabbed a pen and a yellow legal pad and scribbled an equation that took up most of the page. The answer he mapped out made everybody feel, if not exactly happy, at least sufficiently protected.

Just after 4 p.m., seven signatures—some scanned and emailed, others scribbled right there—were attached to the final document on Kavanaugh's laptop. He typed in the addresses of everyone who needed a copy, then waved Griffin over and let the banker click send.

Kavanaugh summed it up like this: "I got them to a place where everybody didn't get exactly what they wanted; they got what they needed."

By "everybody," Kavanaugh meant himself too.

Hollywood and Vine will always be the most famous corner in the history of the film business. But the future of movies is now being constructed at an imaginary intersection: Hollywood and Wall Street. At this crossroads, no one directs more traffic than Ryan Kavanaugh.