Chicago Bears coach Mike Ditka after winning Super Bowl XX in a 46-10 rout of the New England Patriots. Associated Press

For his forthcoming book "Monsters: The 1985 Chicago Bears and the Wild Heart of Football," author Rich Cohen caught up with former Bears coaches and players to find out what made the most fearsome team in NFL history tick. In this excerpt, he explores the team's rise and the stormy relationship between coach Mike Ditka and assistant Buddy Ryan, the brains behind the Bears' intimidating defense.

For Mike Ditka, it must have been maddening. He was the coach of the Chicago Bears but had little control over the defense—he could talk all he wanted but didn't have the power to fire his defensive coordinator, Buddy Ryan, who had worked out a special deal with the team's owner, George Halas. The result was a rift between offense and defense, a rift and a rivalry.

During an epic stretch in the 1980s, when the Bears won 35 regular season games and lost just three, the offense and defense traveled on separate buses, attended separate meetings, followed separate codes.

Ditka and Ryan were often at war. It wasn't an act: These men truly hated each other. It was the energy behind everything; it was there at halftime, at the beginning and end of each practice and game. "Every now and again, when things weren't going well on the field, Mike would come by and make some suggestions," Ryan said. "I'd just tell him to go blank himself, and he'd turn around and walk off."

Bears defensive coordinator Buddy Ryan Getty Images

In an unintended way, this dysfunction helped the Bears: As their offense and defense went after each other, every practice turned into a battle and the players drove each other to the heights of ferocity. Asked to name the best team he faced in 1985, Ditka said, "the Bears."

"When you went out for a normal practice, you wouldn't wear as many pads," safety Doug Plank said, "but when Mike came to town and Buddy was the defensive coordinator, you went to every practice thinking, 'You know what? A game could break out here at any moment. I'm taking everything.' "

Iron Mike

Over time, a football team takes on the personality of its head coach. If he's strong, the team will be strong. If he's weak, the team will be ineffectual.

But what if he's insane?

Standing behind a podium at his postgame news conferences, Ditka looked like a bear and behaved like a bear. His forehead was domed, and his close-set eyes burned. He shifted from side to side, taking his time, deciding which reporter to next raise up and beat down. If a question struck him as stupid, he would grunt and mutter, "Next." He could make "next" sound like a nasty word. Now and then, watching on TV, you'd see a reporter raise his hand, then, fixed in the coach's glare, lower it a little, then a little more, then drop it altogether and stare into his lap. If challenged, Ditka assumed the flat-faced puzzled expression of a bear in a documentary, a grizzly that has caught an interesting smell in the wind, that has reared back on his hind legs, paws dangling, searching for prey. Next. He was a Kodiak rooting through trash on the edge of a national park. He was a grizzly enraged by a swarm of bees.

If asked, after a loss, "What went wrong?" he might grimace and say, "You saw it. We stink." Following an especially bad loss, he said, "I'd be surprised if we won another game." But if the team won, the news conference was raucous. Ditka was still a bear, only now he was a happy bear shredding through picnic baskets at an ill-tended campsite in the Adirondacks.

Ditka was an expressive man, a fist pounder, less like the cerebral masters of the game than like his father, a union boss from western Pennsylvania. He would be calm one minute, then throw a clipboard the next. He said what he thought in the no-nonsense way of the political fixer. When I spoke to Bob Avellini, a Bears quarterback who battled with Ditka, he said, "If the people only knew the truth about their hero Iron Mike: He called plays like a drunken fan."

Of course, they did know, and that is why they loved him. Ditka personified the town and its fans, many of whom were indeed drunk.

Former Bears general manager Jim Finks once described Ditka's method as "Ready, Fire, Aim."

The Genius

Buddy Ryan grew up in Oklahoma in a four-room house without plumbing. He saw action in the Korean War, played football at Oklahoma A&M and, less than a year after graduation, began coaching. Everywhere he went, his defenses hurt people, and his teams won.

In 1978, when he joined the Bears' Ryan was 45, a barrel-chested, theory-stuffed genius. He wore wire-frame glasses and was constantly sticking his finger in the faces of his players, yelling, smirking or brushing the sandy hair from his fierce eyes.

He knew all the tricks of the cult leader, how to sweeten the hours of pain with a scrap of praise, a hand on the neck, a tap on the helmet. In Chicago, he was at the center of worship. Charismatic, intense. You'd follow him to the edge of your strength and sanity because you wanted to be acknowledged. It didn't matter where you were drafted or what you got paid: Buddy made you earn your spot. Everyone started at the bottom, where you were mocked and humiliated, name-called and worked over, until he could see you had broken and were ready to submit. Then he remade you into a killer, a kamikaze who would fly into the aircraft carrier.

"Buddy operated by numbers," Plank said. "There were no names. You were either an adjective, and not a very complimentary one, or you were the number on your jersey. I was 46. Being a number was an honor. It meant you weren't an adjective. Here comes this master sergeant from the Korean War and he started to develop and encourage pride in being part of a special unit, a defensive squad."

In his first years in Chicago, Ryan was coaching mostly mediocre players. On many days, the Bears were outclassed. To compete, he had to improvise. "He was experimenting with defenses," Plank said. "He was going wild, looking for some way to generate a pass rush. You'd go into a meeting and see a bunch of crazy formations on the board. He'd go through each and say, 'OK, here's what we're going to try.' And someone would say, 'What do you call it?' Buddy didn't use X's and O's.

"When he put things on the board, it was numbers. He named formations after the number in the center of the formation. So one morning we go in and sure enough there's a new defense with my number in the middle: the 46."

In the standard 4-3 defensive alignment, the offense's center usually wasn't "covered," meaning no one lined up directly in front of him. This usually allowed the center to double-team a pass-rusher. But Ryan moved a linebacker to the line of scrimmage, then shifted Plank into the gap left by that linebacker. This meant none of Ryan's rushers could be double-teamed.

On a blitz in Ryan's defense, another linebacker or safety might creep up to the line and hide behind a big defensive end. As a result, there were often more rushers than blockers, which is why, in 1985, it often looked as if the Bears had too many players on the field. Buddy called the hidden blitzers free runners. "Confuse the offense until they have no idea where you're coming from—that is what creates a free runner," Plank said. "A free runner is an unblocked defensive player, and he gets to the quarterback so much faster…When a free runner hits the quarterback, the quarterback flies through the air."

In fulfilling an age-old playground fantasy, Ryan had decided to hell with it, and seemingly sent all his guys after the quarterback with a simple mission: Nail him. Rather than try to cover everyone, Ryan decided to short-circuit the offense by taking out the quarterback. As boxers used to say: Kill the brain, and the body will follow.

"Football is chess," Plank said. "You can capture all my pawns, but if I tip over that king, I win."

'Brace for impact'

Ryan's quarterback-destroying creation, the 46 defense, made its debut in 1981, six days after a terrible 48-17 loss to the Detroit Lions. Ryan felt a special urgency: The Bears were about to face the best offense in the NFL.

I recommend this game, played Sunday, Oct. 25, 1981, for study by future generations. Here you had the soaring, pass-drunk offense that Don Coryell devised for the San Diego Chargers, with quarterback Dan Fouts sending a magnificent array of receivers downfield, meeting the 46 in its first sketchy incarnation. Elegant precision faces the howling mob, 11 brutes with maces and helmets, barbarians wandering in the black forest of Soldier Field. It's the dialectic of history: When a system becomes arrogant, a competing system will arise to defeat it.

"As organized and experienced as that group of players were from the Chargers, they'd seen nothing like it," Plank said. "Mad dogs. Wild men. Coming from every side. A jail break. By the end, Dan Fouts did not know where to look: Should he try to find the open man downfield, or should he simply brace for impact?"

It was this confusion, planted in the mind of the quarterback, that made the 46 hum. It wasn't merely pressure that devastated the offense; it was the perception of pressure. Even on plays in which the linebackers dropped back, the quarterback, sensing the rush that wasn't there, hurried himself into mistakes. In this way, the 46 made even the best quarterback defeat himself by turning his own anxiety into a weapon.

The 1-6 Bears beat the 5-2 Chargers 20-17 in overtime. For Fouts, it was among the worst games in a Hall of Fame career. He completed 13 of 43 passes and was intercepted twice. A casual fan might believe he had just seen an upset, a fluke, but it was actually the start of a new era. "We were going wild in the locker room," Plank said. "We were screaming and shouting and all thinking the same thing: 'My God, this can work.' "

Every week, there was a new feature or trick as players learned the intricacies of the 46: how to cheat, where to fake, when to go full-tilt at the quarterback. At first used in spot situations, it became the Bears' standard defense. It peaked in 1984 and 1985. By then, thanks to draft picks and acquisitions, the Bears had great players, including future Hall of Famers Mike Singletary, Dan Hampton and Richard Dent.

There were dominating defenses before 1985 and there have been others since, but none has been quite like the '85 Bears. In the course of 16 games, they gave up fewer than 13 points a game. In their first two playoff games, they allowed zero points. There were games in which the other team barely breached Bears territory.

A few defenses have had comparable numbers, most prominently the 2000 Baltimore Ravens. "You can come up with comparative stats," Singletary has said, "but the best way to tell is to take out the film of any team you want to compare us with: the Steel Curtain, the Purple People Eaters, the 2000 Ravens. Watch them. They're tremendous. Now put the '85 Bears film on and don't say a word. Our film will talk to you. What will it say? You'll know when you see it, because the film does not lie."

Ditka once knocked Buddy Ryan, saying, "On offense, you have to be smart. On defense, you just have to be brutal." It was a put-down, and it wasn't true. In Chicago, the innovations, the big strategic thinking, all came on the brutal side of the ball. The '85 Bears were thrilling on offense but they're remembered because of their defense.

The End of Buddy Ball

As Super Bowl XX approached, some fans worried that the Bears weren't taking the New England Patriots seriously enough. But Chicago had already played New England—in the second week of the season, a game in which they sacked Tony Eason six times and knocked him down constantly. They beat him up and put a fear in him that, according to Bears defensive tackle Steve McMichael, never went away.

Hampton said he knew the Super Bowl would be a romp the Wednesday before the game, when he watched Eason at a news conference. He could tell just by looking at the quarterback's eyes. Worried, scared, he hadn't come to fight. He was hoping only to survive.

The Bears had a final meeting the day before the big game. Ditka said his piece, then the offense and defense split up for separate discussions. Ryan went through the game plan, then, at the moment when he would normally offer some parting wisdom, just stood quietly, as if considering. There had been rumors. Everyone had heard them during the playoffs: that Ryan, after four years of battling Ditka, had finally been offered a head-coaching job of his own and would soon leave for Philadelphia. If true, this would be his last game as a Bear, his last at the helm of a defense he had shaped in his own image. Ryan was more than a coach. He was the leader of a sect, where hitting was a ritual and concussing was a triumph and getting concussed was a sacrifice. For many of these men, football was Buddy Ball. Playing for an ordinary coach was hard to imagine. And yet they weren't naive. They knew it was the same for coaches as for players: Careers in the game being vanishingly short, you take the opportunity.

Ryan admitted none of this; talking about next year while the fate of the current season is yet to be decided is taboo. But he let his players understand the truth in his silence, his lumpy awkwardness. Then, when each man had stopped and considered and realized—the end of Ryan would be the end of the elite unit, the end of the ethos—he cleared his throat, pushed his glasses up his nose and said, "No matter what happens after tomorrow, you guys are my heroes," then walked out.

There was a moment of silence. It distended. It went on. In it, you could hear sniffles and sobs and great big men weeping, tears flowing down thick gleaming faces. "Guys were sniffling and crying. Real quiet," said Ron Rivera, a backup linebacker and the current coach of the Carolina Panthers. "Then all of a sudden, out of nowhere, McMichael goes, 'What a bunch of crybabies. We're getting ready to play the most important game of our lives, and all you guys can do is whine about this?' And he grabs a chair and throws it across the room and it sticks in the chalkboard."

Hampton jumped to his feet beside McMichael, screamed, then drove his hand into the film projector, which busted into gears and springs, and the men, whipped into a frenzy, charged out of the room, which is exactly how Ryan intended it.

As soon as the Bears defense got on the field, they began to terrorize Eason. He had been a star in college at Illinois, 6 feet 4, 212 pounds, a cannon for an arm. The Patriots had drafted him first in 1983. He was at the beginning of a seemingly fine career. But the Bears had him spooked. "His eyes were bugging out," said Dave Duerson. "He was terrified, really, every snap he was on the field. We were way inside his head."

For a quarterback, playing against the 46 was a bit like surfing: If you didn't want to look like a fool, you had to get beyond the break, into the calm water. But Eason spent the entire afternoon close to shore, dashing here and there as the rollers broke over his head. The worse it got, the tighter he played; the tighter he played, the worse it got. He was chased, knocked down, sacked, intercepted. A nightmare, a humiliation watched by millions of people.

Tony Eason is the only starting quarterback in Super Bowl history to finish the day without a single completion. He finished 0 for 6, with three sacks and a fumble. ESPN rated his performance the worst in Super Bowl history. When the Patriots offense came on the field late in the second quarter, Eason stayed on the bench.

A few weeks later, when Ryan was introduced as the new coach of the Eagles, Ditka was asked if he was happy that Buddy was leaving, "Happy? No," Ditka said. "I'm not happy. I'm elated."