METAIRIE, La. -- There's a certain yin-and-yang quality to the New Orleans Saints' defensive coaching staff now that senior assistant Dennis Allen has been paired with coordinator Rob Ryan.

Or maybe it's an "Odd Couple" quality.

Just about everyone asked about what Allen will bring back to New Orleans after four years away as the Denver Broncos' defensive coordinator and Oakland Raiders' head coach mentioned Allen's attention to detail or his calming influence.

Dennis Allen was fired by the Raiders after going 8-28 as their head coach and has rejoined the Saints' staff as a senior defensive assistant. Derick E. Hingle/USA TODAY Sports

As beloved as Ryan is by his players, he's rarely defined by either of those traits. Ryan is known more for his dynamic personality and mad scientist approach to his playbook.

"Coach Ryan, he is passion," said former Saints cornerback Jabari Greer, who played for both men at different times. "And that passion rubs off on his players. They want to play for him, believe in him, trust in what he's doing. He's a creative force, and he puts his players in great position.

"But as far as the details that it takes for a player to execute that certain assignment ... I believe Dennis Allen will do a great job of conveying exactly what Rob Ryan is looking for. [Allen] was extremely prepared, and he prepared us for every situation."

Safety Kenny Vaccaro, who has just begun working with Allen, gave a similar assessment.

"Rob's gonna call the calls, Rob's gonna do the scheme. DA just helps us put it in perspective," Vaccaro said. "Rob's a great defensive coordinator. ... But Rob's not like a technique, 'This is how you do it' guy. He's more of a mad scientist. DA just whips up all the stuff for him.

"[Allen] is a really, really smart coach. I'm thankful to have him, and I can already tell I've progressed since he got here."

Former Saints and Cleveland Browns linebacker Scott Fujita also once used that "mad scientist" description to illustrate the way Ryan works feverishly through the night to come up with new wrinkles.

However, Ryan's playbook is being pared down significantly this year to help cut down on all the assignment and alignment errors that plagued the defense last year. The Saints collapsed from fourth in the NFL in yards allowed in 2013 to 31st.

Becoming more detailed and efficient was also part of the impetus behind bringing back Allen, who served as the Saints' secondary coach during their 2009 Super Bowl run. Head coach Sean Payton created a new role for Allen as "senior defensive assistant." At times, Allen will address the entire defense in meetings, but he's primarily working with the safeties.

Ryan has so far publicly embraced the new dynamic, bluntly acknowledging, "Hey, when you finish 31st in the league, I got a lot to clean up. And I'm happy to have a great coach like Dennis with me -- and our other great coaches."

The 2015 New Orleans Saints defense is on pace to be among the worst ever. Derick E. Hingle/USA TODAY Sports

Ryan laughed, though, at the notion of a calming influence/mad scientist pairing.

"I don't know, hell, I think he's a great guy just like me," Ryan said. "The bottom line is he's an exceptional coach, he's a detailed guy and he's fantastic for us."

Allen, who worked under coordinators Gary Gibbs and Gregg Williams in his first stint in New Orleans, rapidly climbed the ranks after leaving in 2011. He spent just one year as Denver's defensive coordinator before being hired as the Raiders' head coach.

He flamed out in Oakland, though, going 8-28. He was fired after an 0-4 start last year.

"I'd say I'm a better assistant coach now that I've sat in that seat where Sean Payton sits," Allen said. "I understand more what he goes through on a day-in and day-out basis. And my job and the job of these other assistants is to help him do whatever we can to be successful."

Allen, left, and New Orleans coach Sean Payton touched base after a 2013 preseason game between the Raiders and Saints. Derick E. Hingle/USA TODAY Sports

Allen agreed with the descriptions of himself as detail oriented.

"I believe in giving players a plan, giving them the tools and the rules that will allow them to go out and have success," Allen said. "And then they gotta go out and be football players."

Greer said that's what Allen was like, most notably during that 2009 season when New Orleans ranked third in the NFL with 26 interceptions. The Saints capped their Super Bowl win with cornerback Tracy Porter's game-clinching interception against Peyton Manning.

Greer credited Porter for seeing a certain tendency by Manning during film study -- and he credited Allen for giving Porter the freedom to act on it.

"He allowed our players to be us ... without stifling it, without making it robotic," Greer said. "Dennis Allen always told me there's two types of guys: There's rulebook guys and there's guideline guys. And he was great at [separating the two].

"He trusted Tracy, knowing that Tracy was a guideline guy. He didn't stifle Tracy's creativity."

The same kind of relationship developed over time in Denver. Allen helped the Broncos' defense ascend from a No. 32 ranking in 2010 to No. 20 in 2011.

"Once we grabbed the small things, we were able to grab and do more things as far as the blitz is concerned," said ESPN analyst Brian Dawkins, a safety for the Broncos in 2011.

Dawkins said players campaigned for Allen to open up a playbook that had many of the same aggressive tendencies that the Saints' defense had under Williams from 2008 to 2010. But first they had to earn it by eliminating mistakes.

Allen left the Saints in 2011 to become the Broncos' defensive coordinator, a job he held for one year before becoming the Raiders' head coach. Ron Chenoy/USA TODAY Sports

Dawkins, who previously played under one of Ryan's closest colleagues, Don "Wink" Martindale, said he envisions a good fit between Allen and Ryan.

"It's an aggressive system, but it's a lot of thinking," Dawkins said. "Everybody has to be on the same page, because when you're not, you can get gashed."

Exhibit A: the Saints' 2014 season.

But Ryan proved his system can work in 2013, when the Saints finished fourth in yards allowed.

There's a chemistry risk involved in bringing back Allen, with his high profile and established bond with Payton. If the Saints struggle, Allen could be seen as a replacement-in-waiting for Ryan.

If it works, though, Payton will be credited for his matchmaking skills.

"I think that relationship's gonna be great," Allen said of being paired with Ryan. "I think we both understand who each other is as a coach. And I think the great thing that both of us have is there's really no place for egos.

"Everybody's got 'em. But it's really about being able to set those egos aside for the betterment of the team."