By Dan Durkin-

(CBS) New Bears coach John Fox’s roots are on the defensive side of the football. Fundamentally, Fox runs a base 4-3 defense, but he’s shown flexibility over his past four seasons in Denver, running 3-4 fronts and requiring offenses to prepare for multiple fronts.

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When Fox got his first head coaching job in Carolina, he brought in Jack Del Rio to coordinate his defense. After one season, Del Rio became the head coach in Jacksonville. The two reconnected in Denver, as Del Rio served as his defensive coordinator the past three seasons, before recently being named the Raiders’ new coach.

As big decisions await Fox, here are some potential defensive coordinator candidates Fox may consider in Chicago.

Mike Trgovac

After Del Rio left for Jacksonville, Trgovac was promoted from the team’s defensive line coach to defensive coordinator, a role he held for the next six seasons. Trgovac has 20 years of coaching experience and currently serves as the Packers’ defensive line coach, a title he’s held for the past six seasons.

With Trgovac as their defensive line coach in 2002, the Panthers ranked third in the league in sacks (39), and rookie defensive end Julius Peppers earned defensive rookie of the year honors. Kris Jenkins also had a career-high seven sacks, earning a first-team All-Pro honors.

The Panthers ranked in the top 10 in both points allowed and total yardage allowed three times during Trgovac’s six years as coordinator.

In his first season as defensive coordinator, the Panthers ranked eighth in yards and 10th in points, and the Panthers won the NFC championship.

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Trgovac was hired by Green Bay in 2009, the same season the Packers made their transition from a 4-3 to 3-4 scheme, helping the team finish first against the run. The Packers have finished in the top nine in sacks in four of the past six seasons and rank fourth overall with 204.

Dennis Allen

Despite being only 42, Allen has 13 years of NFL coaching experience. Allen was also a four-year letterman at Texas A&M, where he played safety. In 1996, Allen was signed by the Buffalo Bills as an undrafted free agent, but he didn’t make the roster.

Throughout his NFL coaching career, Allen has had the opportunity to work under highly regarded coaches like Wade Phillips, Gregg Williams and Fox.

Allen has ties to both Fox — he was hired as defensive coordinator in 2011 when Fox first started in Denver — and new Bears general manager Ryan Pace, as Allen was with the Saints for five seasons, serving as the team’s assistant defensive line coach for two seasons (2006-’07) and their secondary coach for three seasons (2008-’10).

During the Saints’ 2009 Super Bowl season, their secondary had 22 interceptions, returning a league-high six for touchdowns. They sent both safeties — Roman Harper and Darren Sharper — to the Pro Bowl. In 2010, the Saints allowed a league-low 13 touchdown passes and finished fourth in passing yards allowed.

After helping turn around the Broncos from the league’s worst unit in 2010 to the 20th-ranked unit in 2011, Allen was hired by the Raiders as their head coach in 2012. In 2014, he was fired after the team’s 0-4 start, having compiled an 8-28 overall record.

Allen’s known best for running multiple fronts, primarily leaning on 3-4 looks to deploy a creative blitz package.

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Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @djdurkin.