CHICAGO -- When Khalil Mack was traded to the Bears on Sept. 1 -- just a week before the season began -- the pass-rusher became a model for seamless transitions.

After signing the richest deal for a defender in NFL history ($141 million, including $90 million in guarantees), Mack initially joked he needed to "get on the phone with my financial adviser to figure out what I can afford" in terms of housing. It took him less than two weeks to close on a $3.75 million, six-bedroom, 7½-bathroom, four-fireplace mansion in the North Chicago suburbs.

Despite not knowing most of his new teammates' names, he quickly made friends (and fans) in the locker room.

"I'm not trying to be all up on him but ... That's just a guy you want around," linebacker Aaron Lynch said, just a month into Mack's tenure. "If you get into a bar fight, you want him in your corner. You want to hang out with him. You want him at your wedding."

And of course, despite not knowing the Bears' defense, Mack made history by tormenting quarterbacks with a sack and a forced fumble in each of his first four games, the first player to hit that streak in 13 years. Despite missing two games to nurse an injured right ankle, Mack is still tied for the league lead with four forced fumbles.

Entering Sunday night's prime-time home game against the Vikings -- in which the Bears look to fend off Minnesota for the NFC North lead -- Mack is averaging a sack per game. According to NFL Next Gen Stats, Mack has registered a sack on 3.7 percent of his pass rushes. Last season, no Bears player with at least 200 pass rushes had a sack rate higher than 1.8 percent.

But what the 27-year-old Florida native could not account for was just how thirsty the Bears' fan base was for a player like him. On the team's bye week, the former Oakland Raider caught up on errands. He went to Home Goods and Target. Anywhere he went, he was recognized.

"That's the difference [from Oakland] -- it's everywhere," Mack said. "It don't matter where I'm at. It could be a mother of two, and she'll be a fan. And it's random as hell to me."

'They're falling in love'

Mack called the city's fan base "aggressive" -- in a good way. Those who have been here longer say Mack's experiences aren't surprising at all.

"It's a quarterback-driven league, but this is a defensive-driven town," said right guard Kyle Long, a six-year veteran with the Bears. "We have a really good quarterback [Mitchell Trubisky], but we know what the city prides itself on. That's why they're falling in love with a guy like Khalil Mack."

Iconic defenders -- think Dick Butkus, Mike Singletary, Brian Urlacher -- have always been central to the Bears' success. You can't even mention the Bears' sole Super Bowl win, after the 1985 season, without a quick word association of "Bears D."

The historical lack of offensive success -- and absence of true transcendent stars, outside of Walter Payton -- has allowed the defense to shine. Not since Jim McMahon has Chicago fielded a quarterback who galvanizes the fan base. Jay Cutler, Rex Grossman, Jim Harbaugh, Erik Kramer and Jim Miller all flashed promise but were never able to sustain it. Until general manager Ryan Pace mortgaged his team's future by swapping first-round picks with the San Francisco 49ers along with offering two third-rounders and a fourth-rounder to move up and pick Trubisky second overall in the 2017 draft, it felt like the franchise was resigned to the fact that its defensive identity was its only identity.

"In Chicago, you learn real quick how passionate the fans are about defense," Urlacher said. "That's how they've always won. It's cold, it's about to get real cold, and if you don't have a good defense, you're probably not going to win. The fans know that, and that's why they gravitate toward defensive players. So when you get a player like Mack -- well, you're not mortgaging jack crap when you have a guy who is the best at his position in the NFL."

Mack's divorce in Oakland was messy. He missed the Raiders' summer activities and did not report to training camp as he leveraged for a new contract. Mack was by far the Raiders' most talented player, and it appeared management wouldn't budge. When Mack was traded to Chicago, Raiders coach Jon Gruden said in an ESPN interview that "obviously Khalil Mack didn't want to play in Oakland."

Mack quickly fell into a marriage with Chicago, and the honeymoon phase could not be sweeter. In his first public appearance as a Bear, Mack said it felt great "to be wanted." Chicago gave up record-breaking money and draft picks to get Mack: The trade included two first-round picks -- more than the Bears gave up to trade up and select Trubisky in the draft. It felt quintessential Chicago to ask a defensive player to play savior while the rest of the NFL depended on a quarterback to be that guy.

"Man, I don't know how Pace pulled it off," Urlacher said. "I don't know what he did or if he knows something about Jon Gruden or someone in the Raiders organization or what he's got. But two first-round picks for Mack? That's nothing. When you look at the Bears' first-round picks over the last 10, 15 years, and see how good they've turned out. I'm going to go ahead and say they haven't been very good."

Bears are back

After four straight losing seasons and eight years out of the playoffs, the Bears are suddenly relevant. All offseason, talk around the Bears surrounded the jump Trubisky would make in Year 2. Though the Mack acquisition was a vote of confidence in Trubisky that Chicago management believes it can win now, the quarterback, who is on pace to set franchise records for passing yards and touchdown passes in a season, now shares the spotlight with a pass-rusher in the prime of his career who recorded 40.5 sacks over the past four years.

Almost immediately after Mack's acquisition, the Bears began selling T-shirts that read "Midway Mack," while digital billboards sprouted on Chicago's highways welcoming him to town. It seems fitting that the other ubiquitous signage in Chicago is billboards of Urlacher endorsing a hair transplant company. Urlacher, a fearsome middle linebacker, was the last face of the franchise, and the city hasn't truly had a player to rally around like that since he last suited up six seasons ago.

At home games for the past few seasons, it was not uncommon to spot fans wearing more jerseys of former Bears (Butkus, McMahon, Payton, Singletary, Urlacher, Matt Forte and Charles Tillman) than of the current roster. It was as if fans were conveying a message that they want someone new to latch on to. By the Sept. 30 game against the Tampa Bay Buccaneers, there were already plenty of Mack and Trubisky jerseys sprinkled into the mix.

"You'll realize as an athlete, there's nothing better than playing in a city like Chicago, and there's nothing better than winning in Chicago," said Chicago Blackhawks star winger Patrick Kane. "The city of Chicago gets behind a team, whether it was us when we were winning or especially the Cubs; whenever a team makes even a little bit of a run, it feels like everyone gets behind you. And if the Bears ever won, it probably would be even bigger than all of that, because football is so popular."

Mack's Pack attack

Khalil Mack didn't waste any time making an impact with the Bears; he was responsible for three game-altering plays at the Green Bay Packers in Week 1. That included a 27-yard interception return for a touchdown. Here's a look at the play and an NFL Next Gen view of the circuitous route he took to the end zone.

KHALIL MACK PICK-6! 🚨

Madness. 😱😱😱 #CHIvsGB #DaBears

📺: NBC pic.twitter.com/8xeUcitWie

— NFL (@NFL) September 10, 2018

All of this attention still feels foreign to Mack, who was technically a zero-star recruit in high school before getting his only scholarship offer -- to the University of Buffalo. Mack's off-field demeanor is distinctly opposite from how he plays. As the accolades poured in -- in 2016, he became the first player to be voted AP All-Pro at two positions, defensive end and outside linebacker -- Mack shied away from the mainstream endorsement deals or commercials that would make him a crossover celebrity.

He speaks quietly, but he doesn't speak often. He is frequently seen sporting Miami Heat gear, a nod to growing up in Fort Pierce, Florida. The son of Sandy, who is a program specialist for at-risk youth, and Yolanda, a teacher, Mack is family- and community-oriented. This past summer, Mack joined a business group on a bid that would bring yachts to Fort Pierce for repairs. The project also would bring hundreds of jobs to the area.

Mack came to work immediately in Chicago, which earned the respect of teammates.

"I pride myself in leaving here a little later than most," Long said. "But I walk by the outside linebacker room and he's always there."

Most of Mack's tutoring here came from Bears outside linebackers coach Brandon Staley. Teammates say coaches kept things simple for Mack initially, then incorporated more week by week.

"Yeah, it looks easy," cornerback Kyle Fuller said. "But he's making it look easy."

Defensive end Jonathan Bullard offered his take.

"I don't think it's been hard on him," Bullard said. "Maybe in coverages and dropping, it's hard for him, but doing what he does for us -- getting to the quarterback -- he has no problem. When you're the best at what you do, pass rushing, either you can do it or you can't."

'He still takes it so seriously'

Urlacher, who said he hasn't met Mack personally but texted back and forth with the new face of the defense after he was acquired, noted that Mack's energy is contagious.

"No. 1 is attitude," Urlacher said. "On every play he can wreck a game. He can wreck a game or wreck your game plan in one play. His ability to get to the quarterback, his ability to get to the run -- if you put one guy on him, he's going to make a play. Sunday [against the Detroit Lions] he ran over two guys and still got the sack. He has this attitude that the whole defense has too: We know we're better than you. Most importantly, they're having fun. You watch that defense play and those dudes are having a good time."

The defense, led by coordinator Vic Fangio, was already good before Mack arrived. It remained dominant in the two games Mack missed (albeit against the hapless New York Jets and Buffalo Bills), allowing a total of 19 points.

Mack even brings energy to practice. When the whistle blows for a defensive period, players used to jog to the ball. Mack sprinted. Now, everybody sprints.

"He loves the game, but he's not about any funny business," offensive lineman Charles Leno Jr. said. "When he's here to work, he's here to work."

#Bears tape: Khalil Mack beats the TE chip and then the OT for the sack.

Pretty ridiculous. Enjoy.#DaBears @ChicagoBears pic.twitter.com/6uuX2Zt78B

— NFL Matchup on ESPN (@NFLMatchup) November 12, 2018

Lynch agreed.

"He's the richest man in the NFL, and you'd think maybe he'd coast and still play good," Lynch said. "But he's still playing like he's trying to get another $140 million contract. So that's what's cool for me, personally. Seeing how he still takes it so seriously."

Urlacher sees Mack's passion.

"Watching him play, he's got one speed," Urlacher said. "He goes as hard as he can, and then if he needs a break, they take him out. And then he does it again. I just admire the way he plays and how aggressive he is out there."

What's not lost on teammates is why Mack landed in Chicago. He was in a contract dispute with the Raiders because he worked to become one of the most elite players at his position and hadn't been compensated as such.

"We hope everyone gets what they deserve, and he deserves every penny of what he got," Long said. "If we were all in that situation, we'd all do the same thing."

Added Bullard: "He deserves it, he stood for it, and that's important for us as players. The top guys standing up makes it good for everybody. And when you're producing the way he is, somebody is going to give you what you think you deserve. I'm glad it's us."

After his initial surge, Mack was slowed in a Week 6 loss to the Miami Dolphins. Mack sustained an ankle injury, which quieted him on the field and kept him out of practice the following week. He returned against the Lions in Week 10 and sacked Matthew Stafford twice. Perhaps things will slow down for him as the season goes on -- or maybe he'll just adjust to his new reality as the face of a franchise.

"The advice I would give him is enjoy it, soak it up," Kane said. "People are great here. They might stop you and say hi in the street, but they're not going to try to take up 20 minutes of your time; they'll let you do your thing."

And Mack's thing is wreaking havoc on defense, something his new city adores.