When it comes to toughness in sports, most envision the macho athlete who spends countless hours in the weight room. And while that image may apply to a handful of the athletes on this list, toughness in sports is better captured through the mental aspect. Dedicating time to the gym is a requirement for every athlete on this list, in fact some of the tough ones have been forced to spend even more time in it—behind the scenes—rehabbing from injury. But on game days, mental toughness separates the good and the great, and it's no coincidence that nearly every athlete on this list is among the elite in his or her respective sport. It’s the moment when an athlete puts the squad on his or her back and motivates teammates to dig a little deeper for the betterment of the franchise. The selfless leaders who demonstrate that toughness reliably are the ones who are praised, and while they fight for the name on the front of the shirt, fans begin to love and remember the name on the back.

Most NHL tough-guys have their roles limited to goons, but the two that cracked this list bring a well-rounded game to the table, and it’s no surprise they represent the big bad Bruins. While each one of the following 20 athletes possess superhuman talent, they find themselves on this list based on their shear desire and will to continue to battle for their respective club. Most of all, nearly every one of these players is highly regarded by those in the sport. Some may hate playing against them, but you can bet they’d love to have them suit up for their squad. If others in the sport followed suit, the competitive level would soar and make viewing even more exciting for fans.

Here are the current top 20 athletes in sports.

22 20. Luke Kuechly – Carolina Panthers

From the moment Luke Kuechly began his career as a Panthers starter—filling in for one of the faces of the franchise Jon Beason—opposing teams began to shy away from running the rock toward him and the Carolina defense. It’s a testament to his preparation and accompanying football instincts. Kuechly led the league in tackles last season and ranked fourth in that category in 2013. The two-time All-Pro linebacker is expected to continue to anchor the Carolina defense for years to come as the Panthers decided—duh—to pick up his fifth-year option back in April.

21 19. Milan Lucic – Boston Bruins

The majority of those considered tough NHLers are delegated to the role of goon on their respective squads, but Milan Lucic is the total package; he can drop them if necessary, or help orchestrate a goal when the Bruins are in dire need of one. In 2012, his NHL peers named him the league’s toughest player, and the runner-up on that list—fittingly, his teammate—comes in on this top 20 at 15.

20 18. James Harrison – Pittsburgh Steelers

Like Lucic, Harrison enjoyed the best days of his career while wearing black and yellow for one of the renowned sternest teams in NFL history—led by Dick LeBeau. But it was during his short stint in Cincinnati that the whole world caught a glimpse of how powerful and intimidating he really is.

During 2013 training camp, a pair of young Bengals hopefuls decided an arm-wrestling competition would be the best way to settle their debate and help anoint the stronger player. The winner was awarded a bout with James Harrison, which lasted all but two seconds, and was broadcast through the HBO cameras on Hard Knocks. Harrison continues to post Instagram videos demonstrating his insane strength, including one of which documents him lifting a 135-pound barbell with one arm.

19 17. Anquan Boldin – San Francisco 49ers

Anquan Boldin’s ex-head coach in San Francisco Jim Harbaugh said he’s as tough as any player at any position in the NFL, both mentally and physically. And you can notice exactly what Harbaugh echoed when you see Boldin make difficult acrobatic catches, break tackles, and block. When his former team, the Ravens, signed another hard-nosed veteran receiver last offseason—seemingly to fill the void left by Boldin—pundits immediately began to draw comparisons between the two. That player comes in at number 11 on this list.

18 16. Marshawn Lynch – Seattle Seahawks

If there were one NFL player you’d bet would make this list, it would be Beast Mode, Seahwaks thumping running back Marshawn Lynch. Even Panthers linebacker Luke Kuechly—a fellow top 20 toughest athlete according to this list—said Lynch was one of the hardest to bring down. The New Orleans Saints can attest to Kuechly’s claim, as they know all too well how difficult a task it is to bring down Beast Mode. In fact, the Saints helped give birth to Lynch’s nickname when they allowed him to run wild on their defense in a 2011 wildcard playoff game. I can imagine skittles have been banned from the Saints facility ever since.

17 15. Zdeno Chara – Boston Bruins

Playing physical hockey is synonymous with the Boston Bruins organization, so it comes as no surprise that two of their players made this list. Zdeno Chara was voted the second toughest player in the NHL by his peers in 2012, sandwiched by two other Bruins in first and third, the former finds himself on this list. If those same peers held a vote for toughest fighter, Chara would definitely be in contention for the top spot. The Bruins captain has continuously embarrassed opponents brave enough to drop the gloves with him.

16 14. Jimmy Butler – Chicago Bulls

When the Bulls drafted Butler with the final pick of the first round of the 2011 NBA draft, they hoped he would fit seamlessly as a role player for Tom Thibodeau’s defensive-minded squad. Chicago would soon realize Butler’s ceiling was far loftier than role player. This past season he averaged 20 points per game (over 45 per cent) while dominating the defensive side of the floor. He plays with grit, and you would imagine this attitude was instilled in from the adversity he faced as a child. Butler was homeless as a teenager, he was kicked out of his house by his mom at 13, and subsequently bounced from home to home. Now, he’s the reigning NBA's most improved player.

15 13. Terrell Suggs – Baltimore Ravens

T-Sizzle is the guy we know on Sundays. He’s the alter ego of Terrell Suggs, the gentleman, as he refers himself off the field, but T-Sizzle is no gentlemen; according to Suggs, he’s a “caveman, a barbarian.” And that’s the type of approach Sizzle, or Suggs, takes to the gridiron. He surpassed the career 100-sack mark this past season en route to 12 sacks, his best statistical number since 2011. Even after so many years in the league, Sizzle still strikes fear in opponents.

14 12. Ben Roethlisberger – Pittsburgh Steelers

There’s a reason they call this guy Big Ben. Not only has Roethlisberger taken some of the biggest hits ever—especially playing against Baltimore and guys like Suggs twice a year—and labored back up, but he’s easily become the toughest quarterback to bring down. His strength and ability to shed and elude pass rushers has become his trademark. Big Ben is a two-time Super Bowl Champion, and he embodies what it means to be a Pittsburgh Steeler.

13 11. Ndamukong Suh – Miami Dolphins

If this list recognized the world’s dirtiest athletes on the field, Ndamukong Suh would have landed in the top five. He’s widely regarded as the NFL’s dirtiest player after having accumulated a myriad of fines for his antics on the gridiron. Most of the time, he’s tossing linemen aside in hot pursuit of quarterbacks. Due to the latter, the Dolphins made him the highest paid defensive player in the league earlier this offseason; that means Suh joins forces with Cam Wake and Olivier Vernon along the team’s defensive line.

12 10. Steve Smith – Baltimore Ravens

The man who filled the role of tough, veteran receiver in Baltimore, and the guy who told Aqib Talib to “Ice up, son” in his 13th and final year as a Carolina Panther is just 5-foot-9. Despite his size, if you ask anyone around the league, he might just be the toughest and most feared receiver out there. Like many said about NBA legend Allen Iverson, Steve Smith is pound-for-pound one of the greatest ever. And even when most believed his career was over at age 36, he strung together one of the best years of his career, and eclipsed the 1,000-yard plateau while scoring six touchdowns.

11 9. J.J. Watt – Houston Texans

The NFL has never seen a player with a freakish combination of size, strength, and athleticism like Watt. He flirts with 20 sacks each season, and still manages to intercept passes, and more impressively, catch touchdowns as a designated goal-line tight end. You would think he would be satisfied after winning Defensive Player of the Year this past season, but instead, he purchased a cabin in the woods and promised to live and train there throughout the offseason.

10 8. Serena Williams - Tennis

Serena Williams has dominated the field in women’s tennis for nearly two decades. She earned the top ranking in women’s tennis on six different occasions, and has over $67 million in career prize money. In 2013, she became the oldest World number one player in the sport’s history. She may go down as the greatest women’s player of all time, and according to Maria Sharapova, the difference is her competitive edge. “She doesn't like to give free points and free games,” said Sharapova in 2013. “No matter the score she wants to win those games and those points, whether she's down a break point or up a break point or whatever it is.”

9 7. Clay Matthews Jr. – Green Bay Packers

With most tough athletes, the situation they find themselves in has little barring on the final result. They find ways to battle through adversity, and for Matthews, he was asked to slide inside to middle linebacker last season and found a way to impact the game as powerfully as he did while hunting quarterbacks. His passion permeates throughout the Packers defense and lifts teammates to perform with similar desire.

8 6. Dwyane Wade – Miami Heat

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When most think of the term toughness, they think of strength and power. But Wade grabs the sixth spot on this list for his mental toughness. In fact, Metta World Peace—formerly known as Ron Artest—selected Wade in his all-decade mental toughness team, a list he tweeted to the world in 2013. “Flash” has repeatedly bounced back from injury and continues to give it all for his one and only team, the Miami Heat. That’s something the front end of the 2003 stellar draft class can’t say.

6 5. Floyd Mayweather Jr. - Boxing

Regardless of how he’s mustered an unbeaten boxing record, the accomplishment alone proves Mayweather is one of the greatest pound-for-pound fighters in history. And while many boxing fans weren’t too fond of the outcome of his most recent bout, and more specifically the manner in which he defeated Manny Pacquiao, Mayweather demonstrated his prowess as a defensive fighter.

5 4. Rafael Nadal - Tennis

When watching Rafael Nadal play a five-set grand slam and prevailing, no better word comes to mind than warrior. Like a bruising running back, he thrives as a match progresses, and seems to use the feeling of outlasting an opponent as lifeblood. His aggressive and relentless style of play has helped him close the gap on legend Roger Federer, and he might just surpass him when all is said and done. There’s a good chance he takes a similar, aggressive approach when playing poker.

4 3. Tony Allen – Memphis Grizzlies

If the world didn’t know that Tony Allen was already worthy of such an honor, he let them know: “First team all-defense,” he shouted after making a clutch play against the Golden State Warriors in a recent playoff game. If that wasn’t enough to garner recognition, he received admiration from one of the all time greats earlier this season. Future Hall of famer Kobe Bryant praised Allen, saying he had never heard him call for help on a defensive sequence. Bryant also spoke about his unique competitive spirit. “He plays harder than everybody else defensively,” said Bryant. “He has a competitive desire to compete individually. He likes taking the challenge.”

3 2. Russell Westbrook – Oklahoma City Thunder

With his partner in crime—Kevin Durant—laboring for most of the season, Russell Westbrook became a man on a mission and attempted to single-handedly propel the Thunder into the postseason. The day after undergoing surgery on his face, Westbrook registered a 49-point triple double. All together, he recorded a mind-boggling 11 triple doubles this season, seven more than runner-up in that category, James Harden.