ONE OF HIS friends lovingly describes Theo as a "dick," which covers a multitude of behaviors. Epstein creates a movable locker room wherever he goes, where the most valuable currency is the ability to give shit, and to take it. After a game at Wrigley this summer, he walks across the street to the baseball operations office. The room is full of proprietary information, which the Cubs closely guard. "The only thing that is on the record in the whole office is that picture of Jed up there," Theo says, pointing as everyone laughs. Hanging high on the wall is an enormous photograph of Jed Hoyer posing in a field, in front of a turquoise pickup truck, with another man. Their feet are kicked back, like they're about to kiss in an Audrey Hepburn movie. It's Jed and his brother-in-law. They married twins, who'd posed for the same photo moments before. Jed did it as a joke, and it hit Facebook or Instagram, which meant Theo eventually saw it. Now it's blown up on the wall.

Theo's friends love to tell stories -- stories that define him to them as strongly as his use of data does to baseball fans. When the guy who wears the Cubs mascot costume started taking his job a little too seriously, Theo stole the head and then took a series of dirty photographs. In 2004 during spring training, he put laxatives in a bowl of hummus. The young guys knew to stay away from any appetizers Theo brought to the rental house, but an old baseball hand dug in and paid the colonic price. Nearly three years ago, he and a bunch of guys celebrated Hoyer's 40th birthday at one of their favorite Chicago restaurants, called Girl and the Goat. Once the evening got the better of them, Theo climbed the tall rotating neon goat in the place, nearly falling, cutting his right shoulder in the process. He posed for pictures with his wound, laughing at the imagined headlines: "Cubs President Felled by Curse of the Goat."

Now, after getting his dig in on Jed's photo, he sees one of his youngest employees wearing green slacks. Theo grins, pauses and then says, "He's waiting to win the Masters to complete his suit," and everyone laughs, including the butt of the joke. The one-liners are always pointed and often baseball-nerd specific. In 2002, Adam Grossman, currently a Red Sox vice president, wanted to make a good impression on his first day of work. He wore his best college-frat-guy clothes, complete with trendy loafers, and introduced himself to Theo by the batting cage. They shook hands. Theo looked down at Adam's feet.

"What would John McGraw say about those shoes?" he deadpanned.

Later that season, he stood on a desk and performed a dramatic public reading of the earnest cover letter Grossman wrote to apply for his job, leaving Grossman wanting to crawl beneath the floor. Hoyer had to come in behind Theo and make sure the kid was OK.

When Theo is mad, he likes to break stuff. Back in Boston, they all remember one night after a tough loss when he waved around a driver in the office. He set up a ball with the intention of crushing it down a narrow corridor, either into an empty office door or, better yet, shattering a window. With folks crowded around, he gave it a go, and the ball hit a concrete pole, then caromed at an impossible angle ... straight into the forehead of Ben Cherington, the VP of player personnel. They heard the moans first. Blood gushed from the wound. Minutes later, Theo went outside to meet Ben's irate wife, who'd planned on picking her husband up that evening to move stuff to their new house. "Don't be mad" is how Theo opened the conversation. Later, he signed the golf ball and gave it to Ben as a joke.

"He can't shut off The Theo," Grossman says.

NOBODY IN BOSTON took more shit than Amiel Sawdaye, who came to the Red Sox in 2002 and is now a vice president of scouting. Sawdaye gave it back harder than anyone else, sometimes literally trading punches with Epstein, wearing the boxing gloves they kept in the office to blow off steam. Around the time Epstein was moving to Chicago, Sawdaye sold his house while buying another that wasn't nearly ready for a move-in. His plan was to take his family to spring training, but a medical emergency with one of his children ruined that plan. He didn't have anywhere to live, so Theo waited to sell his and Marie's place in Boston so Sawdaye and his family could room for free. Despite the pranks, Theo is often thoughtful and generous. Once, Epstein sent a banner of Kris Bryant, which had been hanging on Wrigley Field, to Bryant's father. When a roving minor league consultant, Mike Roberts, lost his wife of 46 years, Epstein invited him on the road with the Cubs -- his first time ever traveling with a big league club, after a lifetime in the game -- and the players' wives and girlfriends made sure to deliver food when Roberts was at home.

If I let my brain follow its path unfettered, it would be kinda ugly. - Theo Epstein

He's always had a deep sense of empathy, of knowing what other people are feeling. For most of his life, he's reflected the energy of the room he's in, able to shape-shift, or more accurately, not able to not shape-shift. If he's talking with Kevin Millar or John Lackey, he can be just as filthy as the crustiest big league ballplayer. With rock stars, he can talk eloquently about the challenges and risks of fame, or really get into discussions of gear. With analytics experts, he can go deep on simulation methodology. He can talk Nantucket real estate with millionaires, yachts with billionaires and reality shows with the interns. "I don't think I'm a chameleon," Epstein says one night. "I can feel where people are coming from, what makes them tick, where they are vulnerable, what makes them feel good about themselves. I get just as much out of it as they do. I love connecting."

It began in part at Fenway, he and his father and twin brother, Paul, often walking to the park for games. Theo not only remembers but still inhabits those long-ago moments: his dad holding his hand through Gate A; the sound of the creaky turnstile; the smell of the brown-mustard packets, the dirt, the grass. Leslie Epstein let each boy pick three things from concessions, either spread out or all at once. Theo would go with a Fenway Frank, a pretzel and a little carton of milk. The company that made the hot dogs was called Kirschner, which became the Epstein family code word for fans who came to games but didn't know baseball. If someone sat next to them who treated it as a social outing, Leslie would say, "K-k-kirschner, boys. Kirschner," and Paul and Theo would explode in laughter. Some days, the boys would play arcade games or go candlepin bowling at Ryan Family Amusements, just down the street from the ballpark.

Twenty-five years later, Theo gave away his first World Series ring to his father, because seeing his dad stare quietly at it felt much better than getting it himself. His strongest memory of the 2004 celebration is watching the other baseball operations people pouring champagne on one another, seeing the look on Johnny Pesky's face. Such moments are fragile, and the state of rapture he craves is only achievable in concert with others. The morning after the Red Sox won in 2004, the team landed and made the familiar drive from Logan to Fenway. Theo gets chills even now remembering the cars pulled over on the side of the road and the Red Sox hats sitting on top of gravestones in a cemetery they passed. An entire city stopped. The living celebrated being alive, and they also remembered the dead.

The next title, won three years later in part by homegrown players Theo's crew found and nurtured -- Lester, Papelbon, Pedroia and Ellsbury, selected in four successive drafts -- felt deep and satisfying in its own right. He longs for that again, and a title in Chicago would combine the best of 2004 and 2007. He's after a feeling, even if he knows better than most how quickly it goes away, and how hard it is to find once it's gone.

ON AN EXCEPTIONALLY hot morning in July, Epstein stands outside his office on the sidewalk near Clark Street, sheepishly explaining why his phone is shattered. He broke it in a fit of anger when the team slumped before the All-Star break and hasn't found the time to get a new one.

All teams are more fragile than people want to admit to themselves.

"If we have a horseshit month, if we lose this lead, they will be paying attention to what time I come into the office," he says. "They will be thinking we got complacent. It's a human phenomenon that there has to be a reason for everything. There almost never is. Inexplicable shit, like flipping a coin or the outcome of a baseball game, we need to tell ourselves a story: This team has great chemistry. This team is tough. You know what? That shit all matters, but it's never the full answer that people want it to be. It's why we have stories about the stars in the sky, and the planets and the seas and gods and mythology. We evolve to a point where we can tell and understand the stories. Some are real and some are not, but we attach meaning to all of them."

This inability to control the most important thing in his life makes him, he admits, something of a junkie, which leads to a life without balance. Attempts by other teams to replicate his analytical process are misguided, because his baseball philosophy in truth comes from a hardwired place in his psyche. More than an exploiter of undervalued markets or an expert at predicting which high school seniors might turn into All-Stars, Epstein is completely unhinged. He obsesses over details, from the draft board to the recruiting video he made while wooing Jon Lester, complete with a fake World Series call by the real Cubs announcers, to the time he spent trolling taxidermy websites to find the perfect stuffed bear for the players' cafeteria. Last year, while the Cubs were building a new clubhouse, he hyperfocused on the number of inches between the couch and the ottoman. "I have dozens of pictures of circular sectionals," he says.

Standing on the street between his office and Wrigley Field, as a few fans hang back waiting for his intensity to fade enough to ask for an autograph -- a popular request is a baseball inscribed with "Reverse the Curse" -- he describes how they go about researching the backgrounds of people the team might want as players. For instance, in the Summer of Find Pitching, he gets a dossier on closer Aroldis Chapman, which includes the allegation of firing a pistol in his garage after an argument with his girlfriend. But the closer, according to outside simulations, raises the Cubs' chance of a title to slightly less than 1 in 4. Epstein is faced with a difficult decision.

Over the course of days, he collects information, weighs it, then makes a call. He sends a pitcher and three prospects to the Yankees and acquires Chapman. Giving up those players will absolutely make the Cubs weaker in the future, which Epstein knows, but the team needs a closer like Chapman to make a real October run.

The trading deadline, he laments over and over, is a "mindfuck." But his rationale is cold: The sign in his office still says Find Pitching.

He enjoys it, however, this hunt for information. It's the part of the job most connected to the questions he asks about himself. He loves the dossiers the scouts put together, full of details about friends and enemies, with copies of incriminating photos floating around the internet for stars like Chapman, and for high school kids, descriptions of their childhood bedrooms. "They write these background reports that all read like Russian novels," he says one day. "I'm telling you, everyone's life is a fucking Russian novel if you dig deep enough. Everyone."

EPSTEIN MIGHT HAVE ended up a writer or a lawyer or a juvenile delinquent, except for three things that happened around the time he turned 12. In the spring of 1985, his favorite baseball computer game on the old Apple II, Micro League Baseball, released a general manager disk that allowed him to make deals and create rosters. The game was just a year old, the first real simulator that emphasized strategy and not hand-eye coordination. Theo created a team of all Negro League players and dominated the computer game. Later that year, when he was 12, he got his first Bill James historical abstract, which came out in December of '85. Ten months after that, the 1986 Red Sox lost the World Series, and so Bill James and Micro League Baseball no longer appealed to him in a purely intellectual vacuum. They gave him a way to put his broken heart back together, combining the emotional and factual for the first time into a worldview. One night this summer, he's asked if any of his success would have happened if he hadn't been 12 in the fall of 1986. There's a long pause.

"Probably not," he says finally.

At Yale, he applied for baseball internships and landed in Baltimore, where he organized a celebration of many of those same Negro League players he got to know on his computer. His fantasy became real when a position in San Diego led him back to Boston as assistant general manager. When Billy Beane decided not to take the Red Sox job, the owners took a chance on the 28-year-old already working down in the basement.

The morning Epstein became the GM, he walked outside his condo near Fenway and found camera crews waiting, and they followed him to work as he reminded himself not to trip, concentrating on the steps. Even now in Chicago, he often tugs at the bill of his cap, a nervous tick left over from when he became a public figure overnight. "I was emotionally 16 when I was 28 and got the job," he says, then going on to describe how he acted in high school. "I was so introverted. I used to follow people home. I just like being anonymous so much that I would follow people home because they didn't know who I was and I could watch them. I know how that sounds. I could not exist but observe. I could put a hat on and follow them."

He nailed the news conference and then went to work. A few hours into the job, his co-worker and childhood friend Sam Kennedy called him.

"What are you doing?" Sam asked.

"I'm just sitting here being the GM," Theo said.

Back at home, Marie bought him an ice cream cake to celebrate his new job, but he stayed so late at the office, the cake melted. That should have been a warning. Those in the baseball ops team chased a title at the exclusion of nearly everything in their lives. They rarely left, working 18-hour days. When they did finally rejoin the real world, they kept talking about baseball, at Theo's apartment, or at a bar, or at one of the neighborhood places where they ate over and over again: tacos at El Pelon or chicken-fried rice at Rod-Dee II. Theo scoured the baseball rulebook for accidental loopholes to exploit, accepting nothing, even coming up with new ways to interview managers, like making Terry Francona manage a series simulation against the smartest data guy in the office. (Francona drew.) They grew up together, Theo, Jason McLeod, Jed Hoyer and Ben Cherington. At the time, only Cherington was married, although he'd end up divorced. The lines between work and home disappeared. "There's a real connection," Hoyer says. "We were each other's families in a lot of ways."

Everything in Theo's world centered on his office in a basement, far away from the main Red Sox office on the second floor. That basement wasn't always used by the Sox. Before, it had been Ryan Family Amusements, where Theo and Paul Epstein went bowling and played arcade games, so that every morning he went to work, Theo plugged into the constellation of memories from his childhood.

Those years were the best of his life.

Then they won the World Series.

Theo called Patriots coach Bill Belichick for advice on how to handle success.

"You're fucked," Belichick told him.