LAKE FOREST, Ill. -- Chicago is having fun again.

Coming off a 5-11 season, the Bears finished 12-4 and won their first NFC North title in eight years. They have a Coach of the Year candidate (Matt Nagy), a superstar (Khalil Mack) leading the No. 1 scoring defense and a promising young quarterback (Mitchell Trubisky).

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The Bears haven’t relished the spotlight like this since the 1985 team that won the Super Bowl.

Nagy’s Bears party inside the locker room in "Club Dub" after victories, participate in offense vs. defense dance-offs on Saturday morning, and have a roster packed with five Pro Bowl players and seven alternates.

And they’re winning. The Bears enter the playoffs having won four straight and nine of 10.

But a lot had to happen for the Bears to become relevant again.

Bottoming out

Bears general manager Ryan Pace inherited an organization in turmoil in January 2015.

The ill-fated Marc Trestman experiment as head coach was over after two seasons. The Bears had fired him and general manager Phil Emery, who was responsible for hiring Trestman to replace Lovie Smith.

Morale was low. The Bears didn’t bottom out at the end of the 2014 season -- they self-destructed.

Ryan Pace had his work cut out for him when he took over as Bears general manager following the 2014 season. Charles Rex Arbogast/AP Photo

Chicago was stuck with embattled quarterback Jay Cutler. Talented wide receiver Brandon Marshall had worn out his welcome and tight end Martellus Bennett was about to wear out his.

The Bears' roster was loaded with aging veterans, and far too few of their recent draft picks were making meaningful contributions.

The only notable holdovers from the previous regime -- to this day -- are right guard Kyle Long, left tackle Charles Leno Jr.., cornerback Kyle Fuller, special teamer/nickel back Sherrick McManis and punter Pat O’Donnell.

The Bears weren’t an overnight fix.

Chicago made its share of mistakes over the next three years, including hiring John Fox as head coach. Fox’s conservative approach did not mesh with the game’s new wave of forward-thinkers, Pace among them.

Worst of all, the Bears routinely were blown out in Fox’s final two seasons, and attendance at Soldier Field dwindled to record lows.

The Bears’ free-agent class of 2015 (Pernell McPhee, Eddie Royal and Antrel Rolle) was a complete bust. Pace’s first draft pick, wide receiver Kevin White (seventh overall), suffered one injury after another. Chicago’s 2016 top pick, Leonard Floyd, battled his own injury issues that prevented him from truly emerging on defense until this year.

The Bears prematurely moved on from kicker Robbie Gould, who since his surprising release prior to the 2016 season has converted 82 of 85 field goal attempts.

But even as the Bears’ record plummeted under Fox (14-34), Pace slowly rebuilt the core of the roster.

The Bears quietly added valuable pieces such as defensive lineman Akiem Hicks (free agent), nose tackle Eddie Goldman (second round, 2015), linebacker Danny Trevathan (free agency), center Cody Whitehair (second round, 2016) and safety Adrian Amos (fifth round, 2015). But Chicago’s rebuild kicked into high gear on draft night in 2017.

Finding a franchise QB

Pace stunned most of the football world by trading up one spot with the San Francisco 49ers to draft North Carolina's Trubisky second overall. After starting for only one full season in college, Pace was convinced Trubisky possessed the ability to spearhead the Bears’ renaissance.

Mitchell Trubisky passed for 3,223 yards with 24 touchdowns and 12 interceptions in his second season. Brace Hemmelgarn/USA TODAY Sports

Following an underwhelming rookie season, Trubisky took a big step in Year 2, passing for 3,223 yards with 24 touchdowns and 12 interceptions in 14 starts. Pace chose Trubisky over Patrick Mahomes (10th overall) and Deshaun Watson (12th overall), and it's likely Trubisky never reaches their level. But the Bears desperately needed a changing of the guard. They could no longer stick with Cutler, who had long outlived his usefulness.

For as much as the Bears craved an instant upgrade at quarterback, Pace had to look at Trubisky through a longer lens. The Bears needed a young quarterback to help lure their next head coach to Chicago.

Pace soon found the answer.

Finding the right coach

The decision to fire Fox was easy. Finding the right replacement, not so much.

Nagy, the 39-year old Kansas City Chiefs offensive coordinator, had called plays in only five games, including a bitter playoff loss, under coach Andy Reid. Nagy, who previously worked for Reid in Philadelphia, was one of the hotter names among 2018 head-coaching candidates.

Matt Nagy's offense has been productive, creative and fun for the Bears this season. Doug Murray/Icon Sportswire

The Bears had done their homework, and they were convinced Nagy was the best fit.

Sensing the Indianapolis Colts were just as eager to hire Nagy, Pace moved quickly. Within a week of jettisoning Fox, Pace had an agreement in place with Nagy to become the 16th head coach in Bears history in January 2018.

The culture inside the building changed immediately.

After convincing veteran defensive coordinator Vic Fangio to return, Nagy next scrapped the Bears’ rudimentary offense from 2017 and replaced it with a version of Reid’s scheme, complete with run-pass options and misdirection that played better to Trubisky’s natural athleticism.

Nagy embraced the idea of working with Trubisky, and vice versa. They met during the 2017 pre-draft process at the NFL combine, and later when the Chiefs hosted Trubisky on a pre-draft workout. Trubisky’s enthusiasm about Nagy’s arrival and the direction of the offense was apparent early in the offseason program.

With both a young head coach and young quarterback under contract, the Bears were able to recruit wide receivers Allen Robinson, Taylor Gabriel and tight end Trey Burton in free agency.

Chicago also prioritized re-signing starting cornerbacks Kyle Fuller and Prince Amukamara. Fuller (seven interceptions) made the Pro Bowl in 2018, while Amukarmara had one of his best seasons with 66 tackles, 3 picks and 11 pass breakups.

Pace also hit on linebacker Roquan Smith, who was drafted in the first round, as well as wide receiver Anthony Miller and guard James Daniels, both taken in the second round. All three were major contributors as rookies this season.

And with 2017 fourth-round picks Tarik Cohen and Eddie Jackson poised for breakout seasons, the Bears turned into one of the league’s most improved teams.

Most predicted seven, eight, even nine wins for the Bears in Nagy’s first season.

But what happened on the eve of the regular season raised expectations even higher.

The Mack effect

The Oakland Raiders agreed to trade former NFL Defensive Player of the Year Khalil Mack to the Chicago Bears on Sept. 1.

Wait ... what?!

Pace swung the deal that ultimately catapulted the Bears into playoff contenders when he sent first-round picks in 2019 and 2020, a third-round pick in 2020 and a sixth-round pick in 2019 to the Raiders in exchange for Mack, a second-round pick in 2020 and a conditional fifth-round pick in 2020.

Khalil Mack had 12.5 sacks in his first season with the Bears. Robin Alam/Icon Sportswire

The next day, Mack became the highest-paid defensive player in NFL history, signing a deal with Chicago that averages $23.5 million per season and includes $90 million in guaranteed money and $60 million at signing.

Instantly, the Bears' defense went from top 10 to top three in the league.

Mack led the Bears with 12.5 sacks and was named NFC Defensive Player of the Month in September with 5 sacks, 4 forced fumbles, 1 interception return for a touchdown, 3 tackles for loss, 4 quarterback hurries and 1 fumble recovery.

Opponents learned it’s virtually impossible to use one blocker on Mack. He wreaked havoc on offenses, freeing up other members of the front seven to attack the quarterback and ball carriers. Hicks in particular benefited with 7.5 sacks in his first Pro Bowl season.

The Bears' defense finished No. 1 in takeaways (36) and interceptions (27) and No. 3 in points off takeaways (107).

And Mack is the driving force behind their elevation from very good to elite.