Some of the most beloved players in NFL history are also the most fearsome. Dynasties were built on defenses with names like the "Steel Curtain" and the "Purple People Eaters"; squads defined by vicious hitters like Jack Lambert and Carl Eller.
Players like these had the kind of reputations, and film, that intimidated opponents and transformed the NFL into the most popular sport in America.
As the NFL takes steps to protect players from head injuries, the biggest hitters of the new era are trying to follow rules without compromising their nature.
These are the guys you can expect to be the hardest hitmen of the 2012 NFL season.
The Packers are probably best known for their high-flying offense led by quarterback Aaron Rodgers, but linebacker Clay Matthews is there to remind the opposition that they know how to play defense in Green Bay too.
In fact, ProFootballTalk named Matthews' fourth quarter forced fumble on Steelers' running back Rashard Mendenhall the play of the game in Super Bowl XLV.
Cornerback Dunta Robinson spent his first five years in the NFL with the Texans, but it was in his last two season with the Falcons that he developed a reputation as a vicious hitter.
In 2010, Robinson was fined $50,000 for an illegal hit on defenseless Eagles receiver DeSean Jackson. Just one year later he was fined $40,000 for an illegal helmet-to-helmet hit on Jeremy Maclin, another Eagles receiver.
Second-year Bears defensive end Julius Peppers is coming off a relatively quiet season, but then again, so are the rest of the Bears.
In his first season in Chicago, Peppers made a habit of terrorizing the quarterbacks in his division—first knocking out Lions quarterback Matt Stafford for six weeks, then getting hit with a $10,000 fine for beating up on Packers quarterback Aaron Rodgers.
Linebacker James Harrison isn't the only Steeler with a pile of fines and a bone to pick with NFL commissioner Roger Goodell. Dating back to a vicious hit on Patriots wide receiver Wes Welker in 2008, Safety Ryan Clark has had a reputation of a big hitter.
It wasn't until late 2011 that he started to attract attention from the league office. Clark was fined $55,000 over two weeks for hits that were deemed illegal—his $40,000 fine for a hit on the Ravens' Ed Dickson was the largest fine of the season.
For well over a decade, Ravens linebacker Ray Lewis has been one of the most feared and physically dominating forces in the NFL. He may be getting older, but Lewis could intimidate on reputation alone for years to come.
Not that he has to, since he's still performing on the field. In November 2011, Lewis was fined $20,000 for a bruising hit on a long-time nemesis—Steelers wide receiver Hines Ward.
In his rookie year in 2010, Giants defensive end Jason Pierre-Paul leveled Lions linebacker Zack Follett with a helmet-to-helmet hit that put him in the hospital.
A little over a season later, Pierre-Paul has gone from special teams tough-guy to difference-making starter for the World Champion G-Men.
In just two years in the NFL, Lions defensive tackle Ndamukong Suh has been disciplined for on-field misconduct five times and has earned a place among the most feared players in the league. Suh has also earned a reputation as a dirty player.
In November 2011, a Sporting News player poll named Suh the dirtiest player in the NFL and he did nothing to dispel that notion when, three weeks later, he was ejected and ultimately suspended for stomping on Packers' offensive lineman Evan Dietrich-Smith during a game.
In 2011, the NFL was dominated by the offensive firepower of the Patriots, Packers, and Saints, but the 49ers proved that it was still possible to win with a serviceable offense and a dominant defense.
The Niners defense carried them to just one play away from the Super Bowl, and the reliably bone-crushing play of linebacker Patrick Willis was a huge part of that defense.
Though he didn't get any specific endorsement deals from the NFL, Steelers linebacker James Harrison has become the poster boy for the league's crackdown on illegal hits.
Harrison was fined over $100,000 last season for illegal hits and served a one game suspension for a brutal hit on Browns quarterback Colt McCoy that left him with a season-ending concussion.
There's no doubt that linebacker Ray Lewis is still the emotional heart and soul of the Ravens, but Terrell Suggs has become the most feared physical presence in Baltimore.
He edged out defensive forces like Jared Allen, Charles Woodson and Jason Pierre-Paul to win the AP's 2011 Defensive Player of the Year award. He's been known to lay people out on the field, but the outspoken Suggs can also make you hurt with a sharp verbal jab as well.