CHICAGO » Brian Urlacher wasn’t sure how dominant he could be any longer, so he’s calling it a career after 13 seasons with the Chicago Bears.

And what a career it was:

— Eight Pro Bowl seasons;

— Defensive Player of the Year in 2005

— A trip to the Super Bowl as 2006 NFC champion.

And now, it’s over. The eight-time Pro Bowler announced his retirement through social media accounts today.

“After spending a lot of time this spring thinking about my NFL future, I have made a decision to retire,” Urlacher said in a statement. “Although I could continue playing, I’m not sure I would bring a level of performance or passion that’s up to my standards. When considering this, along with the fact that I could retire after a 13-year career wearing only one jersey for such a storied franchise, my decision became pretty clear.

“I want to thank all of the people in my life that have helped me along the way. I will miss my teammates, my coaches and the great Bears fans. I’m proud to say that I gave all of you everything I had every time I took the field. I will miss this great game, but I leave it with no regrets.”

Urlacher was the face of the Bears, and he ranks among the best middle linebackers to suit up for a franchise with an impressive list that includes Hall of Famers Bill George, Dick Butkus and Mike Singletary.

In March, Urlacher and the Bears were unable to reach a contract agreement and he became a free agent.

“In the pantheon of Bears, Brian has earned his place alongside Halas, Grange, Nagurski, Ditka, Payton — and yes, Bill George, Butkus and Singletary,” Bears chairman George McCaskey said. “We congratulate Brian on a brilliant career and he will continue to be a welcomed member of the Bears Family in retirement.”

Added receiver Earl Bennett on Twitter: “Great player… Great teammate… Awesome person!!!!”

Former Bears linebacker Hunter Hillenmeyer posted on Twitter: “(at)BUrlacher54 was the most coachable superstar, best locker room leader I ever played with. Proud to call him a teammate for 8 seasons.”

And defensive end Israel Idonije, a free agent, wrote, “It was an honor & privilege to work and learn from (at)BUrlacher54 over the past 10 years. (hash)ThanksBruh.”

Urlacher started 180 games from 2000-2012, and made a team-record 1,779 tackles. He has 41 1/2, 22 interceptions, 16 fumble recoveries and 11 forced fumbles.

Last year, he was slowed by a knee problem and then missed the final four games with a hamstring injury.

Urlacher had posted pictures on Twitter indicating he was working his way back into shape before the split with the Bears. But when they announced he would not be back, it was hardly a surprise.

Urlacher told the team’s flagship radio station at the time that he was not shocked and the offer he received was “more like an ultimatum” in which they were telling him, “Sign this contract or we are going to move on.”

The split with Urlacher was just one of many moves in a busy offseason for the Bears.

They fired coach Lovie Smith after a second straight late collapse left them out of the playoffs for the fifth time in six years, even though they did finish with 10 wins.

They replaced him with the offensive-minded Marc Trestman, hoping he could get the most out of quarterback Jay Cutler, and revamped their offensive line.

On defense, the only starting linebacker returning is Lance Briggs. Veteran free agent acquisition D.J. Williams and second-round draft pick Jon Bostic are expected to compete for the middle linebacker job with Urlacher gone.

A safety with lightning speed when he was drafted out of New Mexico, the 6-foot-4 Urlacher initially lined up at strong side linebacker for the Bears, but lost the job to Roosevelt Colvin. He made the switch to middle linebacker during his first season when Barry Minter was injured, and went on to become the 2000 Defensive Rookie of the Year, the start of a long run that saw him anchor a defense that consistently ranked among the league’s best.

But he clearly wasn’t his old self last year. The speed and quickness that allowed him to wreak havoc for years simply wasn’t there.

Urlacher sprained his medial collateral ligament and partially sprained the posterior cruciate ligament in his left knee during the 2011 regular-season finale against Minnesota, He hasn’t been the same since then.

He barely participated in training camp, had an arthroscopic procedure in mid-August to relieve the swelling, and spent most of the season trying to regain his old form.

Then, he came up lame in coverage on the second-to-last snap of the Bears’ overtime loss to Seattle in early December, an injury that ended his season and, ultimately, his career.

“He was a guy that you respected from a coaching standpoint because of what he could do on the field,” Detroit coach Jim Schwartz said. “I know he was respected by players and among his peers. Different kind of linebacker, you know? There are not many guys who are 6-4 playing middle linebacker. It’s generally a position that shorter guys have had a lot more success, guys like Mike Singletary, who probably wasn’t six feet tall; Ray Lewis about the same way.

“But Urlacher, in a lot of ways, changed the position. His range at the middle linebacker position, the speed that he played with, he was super fast.”

AP Sports Writer Larry Lage in Detroit contributed to this report.