For 11 seasons, Keith Butler worked as a linebackers coach under Dick LeBeau. Last offseason, the Steelers parted ways with LeBeau and promoted Butler.

Naturally, there was trepidation about the move. LeBeau was a Hall of Famer, a defensive innovator, beloved by everyone, and had spent more than a half-century in football. But there was also no denying that those vaunted Steelers defenses of recent Super Bowl runs were a thing of the past.

When the Steelers faced the Seahawks in Super Bowl XL, Ben Roethlisberger was a second-year quarterback who benefitted from having the league's third-best defense. When the Steelers returned to the Super Bowl in 2008, Roethlisberger had established himself as one of the NFL's best young quarterbacks. But the defense had also improved -- to the No. 1 unit in the league and arguably one of the most complete defenses of the last decade. Similar story in 2010, Pittsburgh's last Super Bowl appearance: Roethlisberger carried the offense, but a dominant defense (again ranked No. 1) was that team's hallmark.

But things began to change in 2011. The defense ranked seventh, according to Football Outsiders, but a wild-card playoff loss to Tim Tebow and the Broncos ended the Steelers' season on one improbable 80-yard scoring play.

By 2012, the defense dropped to 13th before falling to 19th in 2013 The Steelers went 8-8 both seasons. Pittsburgh returned to the postseason in 2014, but it was due in large part to one of the league's most explosive offenses. Led by Roethlisberger, Antonio Brown and Le'Veon Bell, that group ranked second behind only Aaron Rodgers and the Packers. Meanwhile, the defense continued to languish, falling to 30th. In more sobering terms, they were third from the bottom ahead of only the Falcons and Saints.

Then, in January 2015, the Steelers and coach Mike Tomlin decided to move on from LeBeau and give Butler, who had passed up opportunities with other teams, the task of restoring Pittsburgh's defense to its previous glory.

Mike Tomlin believes Keith Butler is the man to lead the Steelers defense back to greatness. USATSI

If Butler's first season is any indication, the rebuilding process is ahead of schedule. Again, referring to Football Outsiders' advanced metrics, the defense ranked 11th last season, an improvement of 19 spots. The unit also went from 30th to 13th against the pass and from 17th to 5th against the run.

On the surface, losing key personnel would appear to have complicated Butler's job. Safety Troy Polamalu, cornerback Ike Taylor, defensive end Brett Keisel and outsider linebacker Jason Worilds all retired, and cornerback Brice McCain left in free agency. But veterans Will Allen and William Gay were a steadying presence in the secondary, Stephon Tuitt showed glimpses of dominating along the defensive line, and outside linebacker and first-rounder Bud Dupree played more as a rookie than we were accustomed to seeing during LeBeau's tenure.

Also critical: Butler simplified a scheme that was often described as complicated and intricate under LeBeau, allowing younger players to get on the field sooner.

"He tweaked the defense into things he likes," outside linebacker and 2013 first-rounder Jarvis Jones said last November, via the Pittsburgh Tribune-Review. "We still have many of the old concepts, but (Butler) has simplified things so we can play faster and communicate better."

Defensive end Cam Heyward added: "There were times in the past when we sat more on blocks, and let the linebackers make plays. In [Butler's] defense, we (defensive linemen) have more freedom. ... There are lot more blitzes involved, and there are more opportunities to execute one-on-ones. When we win the one-on-ones, we're a much better, successful team, and that's nothing against Coach LeBeau's defenses."

Simplifying the scheme meant young players were thinking less, playing faster and, ultimately, getting after the quarterback. In 2014, the defense managed just 33 sacks. Last season, they had 48. In terms of FO's adjusted-sack-rate metric, that's an improvement from 21st to 7th.

And while LeBeau was known as the Godfather of the zone blitz and primarily a proponent of the 3-4 scheme, Butler isn't concerned with labels.

"I would consider myself a whatever-it-takes-to-win guy," Butler said shortly after he was promoted. "If it's a 3-4, that's fine, if that fits your players. I think you have to be able to fit your defense around the players you have. With what offenses are doing nowadays in the National Football League, they're playing a lot of three wide receivers and a tight end and a running back, for the most part. In those situations, we're going to be in kind of a 4-3 anyway, but we're still going to be able to run the 3-4 also. It gives you a little bit more versatility, I think."

But as Tomlin has said throughout his tenure -- and reiterated after last season -- football is scheme-dependent.

"We're all limited schematically, in terms of what we want to do," Tomlin said in January, via "I think anybody that's an architect of football schematics, you have what you want to do, a vision of what you want to do, and then you have the reality. And the reality is usually associated with the abilities of the players that you have, the amount of time, or your ability to teach and the way that your opponent stresses you."

The Steelers began rebuilding the defense in 2014, LeBeau's last season. The team drafted inside linebacker Ryan Shazier and defensive end Stephon Tuitt with its first two picks that year, then landed rush linebacker Bud Dupree and cornerback Senquez Golson in 2015. After an injury-plagued rookie season, Shazier came into his own in '15. And Tuitt and Heyward have a chance to be two of the best defensive ends in football. Dupree's raw athleticism can take your breath away but he's still learning the position while Golson redshirted his rookie season after being sidelines with a shoulder injury.

But the Steelers weren't done; in 2016 they used their first two picks on cornerback Artie Burns and safety Sean Davis, two long, athletic talents who, in Butler's defense, could see the field sooner rather than later.

The good news is that Steelers are clearly serious about fixing a secondary that was one of the league's worst as recently as two seasons ago.

The bad news: It's an extremely young group, and it's reasonable to expect growing pains. Gay and free safety Mike Mitchell are veterans, but after that, there could be plenty of inexperience on the field come September. Don't be surprised if Burns and Davis earn playing time immediately, or if Golson plays in sub-packages. It'll likely be a trial by fire for this group, though the upside is once it all comes together, their athleticism and playmaking ability will make the Steelers dangerous on both sides of the ball.

Ryan Shazier came into his own last season. USATSI

Which brings us to the offense. Rare is the story about the Steelers that doesn't begin with the NFL's most potent offense, but if the defense continues to improve under Butler, offensive coordinator Todd Haley won't need to worry about averaging 30 points a game, something the unit was just shy of last season (26.4), when Big Ben missed four games with various ailments.

But here's the thing; a year ago, we were talking about Pittsburgh as a legit playoff team if the defense improved to middle-of-the-pack levels. The group did slightly better than that and the Steelers were a late fumble away from beating the Broncos in the AFC Divisional game. This time around, the expectation is that the Steelers' D will be a top-10 unit, the offense will continue to light up the scoreboard, and the Super Bowl is a realistic expectation. In fact, the most recent odds have the Steelers 12-to-1 to win it all, behind only the Patriots, Packers and Seahawks.

As for Butler's goals, odds aren't necessary.

"Win a Super Bowl the next three years," he said last November. "I have a three-year contract with the Rooneys. I aim to fulfill my contract. I have three sons, and I have two Super Bowl rings. I have to get one more. One of them's gonna be pissed if I don't."