Jared Allen is not your run-of-the-mill, washed-up has-been. He's the most accomplished active pass-rusher in the NFL, and he's not done adding to his legacy just yet.

As a member of the Chicago Bears, Allen is still trying to write what figures to be the final chapter of his NFL career. Last season, his first in Chicago, wasn't pretty. It began with a bout of illness, as pneumonia robbed him of 18 pounds and an appearance in Week 4.

Allen finished the 2014 season with a career-low 5.5 sacks. It was an unusual outcome for a player who's grown so used to double-digit production in that category. Just a few years ago, he registered a ridiculous single-season sack total of 22.0 -- just a half-sack shy of the all-time record.

More from FoxSports

This year is bound to be different, though, and that's because Allen's playing a new position. New Bears head coach John Fox has appointed Vic Fangio, who last coached in San Francisco, to coordinate the defense. The fresh system requires a base transition, so Allen is making the necessary position switch from 4-3 defensive end to 3-4 outside linebacker.

In June, Allen championed the transition as a "fun" experience.

"I didn't know anything about it [playing OLB]," Allen said, per ESPN's Jeff Dickerson, "I obviously do love the traditional [4-3 defensive end role]. I played in a Tampa 2 defense my entire career, so there is a part of me that absolutely loves putting my hand in the dirt and that individual matchup with the left tackle in run or pass, or with the tight end. But this as a football player is fun, it really is -- the different styles of matchups you get and some of the one-on-one rushes it creates are really fun. Ultimately, it's kind of the same stuff, but later in my career it's easier on my body because I'm not technically banging every single day."

Allen has only played defensive end during his entire 11-year career, which has yielded 134.0 sacks (9th-most in NFL history). Given the immense success he has experienced at end, it's somewhat surprising to see him so willing to pick up a new position at 33 years of age.

The switch could have a rejuvenating effect on Allen, who may finally be flirting with father time. With such a storied career coming to an inevitable end without ever reaching a Super Bowl, the veteran may be willing to make any sacrifice as long as it helps the team win.

A recent quote about the Bears' new regime seems to confirm that theory.

"It's phenomenal," Allen told Larry Hawley of WGNtv.com. "I heard a word the other day and it stuck with me and that's authentic. When you walk in the building it's a building about football and about winning football games."

Only three seasons removed from his last Pro Bowl campaign with the Vikings, the pass-rusher could reach the top of his game one more time before going out for good. The motivation created by a waning window of opportunity, combined with the excitement of learning a new position, should allow Allen to tap into his remaining potential.

Allen has been a sleeping giant since becoming a Bear, but bet on him emerging from his hibernation in 2015.

Photo Credit: Nam Y. Huh/Public Domain