John Fox dug into his coaching past to find a new defensive coordinator.

The Broncos on Friday hired Jack Del Rio to replace Dennis Allen as the team’s defensive coordinator, reuniting Fox with his first defensive coordinator from Carolina.

Denver also hired strength and conditioning coach Luke Richesson, who spent the last three seasons on Del Rio’s staff in Jacksonville. Richesson replaces Rich Tuten, whose contract was not renewed after 17 seasons with the Broncos.

Del Rio, a former NFL linebacker, joined Fox’s first staff in Carolina in 2002. After one year in that role, in which the Panthers’ defense improved from the No. 31-ranked defense in 2001 to No. 2 in the NFL, Del Rio was hired to be head coach of the Jacksonville Jaguars.

Del Rio held that job until he was fired in late November. Jacksonville owed Del Rio $5 million remaining on his contract and will pay him the difference between that total and his new salary in Denver.

Del Rio inherits a Denver defense that improved from last in the league in 2010 to No. 20 this year under Fox and Allen, with three players (cornerback Champ Bailey, linebacker Von Miller and defensive end Elvis Dumervil) who were voted into the Pro Bowl. A fourth player, safety Brian Dawkins, made the Pro Bowl roster as an alternate.

“We are thrilled to be able to add such a well-respected defensive coach to our staff,” Fox said in a statement Friday night. “He was an integral part of our turnaround on defense during my first year with the Panthers in 2002. His defenses with the Jaguars have ranked among the NFL’s best, and we are excited he’s a Bronco.”

Del Rio’s defenses consistently ranked among the top 10 in yards and points allowed from 2003-06, but slid from 2007-09. The low point came in 2010, when the Jaguars ranked No. 28 in yards allowed and No. 27 in points allowed. Jacksonville climbed back to No. 6 in yards allowed this season, though defensive coordinator Mel Tucker (not Del Rio, as he had in earlier years) called plays.

Del Rio becomes the Broncos’ seventh defensive coordinator in seven seasons after Allen left the team this week to become the Oakland Raiders head coach. Allen’s second interview with the Raiders was conducted in Mobile, Ala., where NFL coaches and scouts convened for the Senior Bowl.

Del Rio also was in Mobile this week and spent some time visiting with Fox. Fox returned to Denver on Wednesday night, and negotiated with Del Rio and his representatives until reaching a deal Friday evening.

Now the question is how long Del Rio will remain in Denver. No coordinator since Larry Coyer, who held the job from 2002-06, has lasted more than a season.

Other coordinators in that time were Jim Bates (2007), Bob Slowik (2008), Mike Nolan (2009), Don “Wink” Martindale (2010) and Allen. All but Allen were fired, resigned or not retained after a head coaching change.

Such instability at coordinator means every Broncos defensive player other than Bailey and D.J. Williams, both on the team since 2004, has had a different coordinator each season.

“Love the hire, just hope we can keep him around,” Dawkins wrote on his Twitter account Friday night from Hawaii, where he is preparing for the Pro Bowl.

Lindsay H. Jones: 303-954-1262 or ljones@denverpost.com

Jack Del Rio

Age: 48. Born April 4, 1963, in Castro Valley, Calif.

High school: Football and baseball star at Hayward (Calif.) High School.

College: All-America linebacker at USC, runner-up for 1984 Lombardi Award, MVP of 1985 Rose Bowl.

NFL playing career: Saints selected Del Rio in the third round of the 1985 draft. Played 11 seasons for Saints, Chiefs, Cowboys and Vikings.

NFL coaching career: Saints hired Del Rio as strength coach in 1997. Ravens linebackers coach 1999-2001. Panthers defensive coordinator 2002 under head coach John Fox. Jaguars head coach 2003-11 (68-71 record).