The word tough can be defined as able to withstand strain, solid, rugged and formidable among other terms. Certain drivers in NASCAR's premier series epitomize toughness for a variety of reasons.
Drivers can be tough without having a persona that would be described in such a manner. They may just be tough competitors who are formidable contenders for race wins and championships.
Other drivers can have the intimidating factor with their aggressive driving style. When these drivers are running well, they can give a competitor a few extra heart palpitations when they close fast on a car.
Those who succeed as Cup drivers must be able to withstand the pressure of racing at such a high level, so every driver is tough to some degree, in addition to having the ability to wheel the race car.
In this slideshow, drivers who might be considered the toughest in the series will be highlighted.
Brad Keselowski, driver of the No. 2 Dodge for Penske Racing, is young, smart and tough. He is a driver who is calculating, but won't shy away from making aggressive moves.
He is mentally tough, which was evident when he broke his ankle during a testing accident then the following weekend he won a race and went on a streak to win two more races.
Keselowski is always full of the unexpected during an interview. Normally he is very personable, but he can be very outspoken.
This driver is tough behind the wheel because he is always a threat to win. He is currently seventh in the point standings with three wins this season.
Tony Stewart, owner/driver of the No. 14 Mobil 1/Office Depot Chevrolet, can be very tough with his old-school driving style.
If you poke this driver with a stick, so to speak, he is going to come after you. Every driver knows if they mess with him on the track, he will pay you back.
Stewart, a three-time Cup champion, is a wheelman and when his car is fast with a good setup, he will be aggressive on his way to the front of the field.
This is a driver who can be soft as a teddy bear, but also tough with his persona, his desire to race anything anytime and win with a bit of in-your-face swagger.
He is currently sixth in the point standings with three wins this season.
Jimmie Johnson has taken his No. 48 Lowe's Chevrolet to five NASCAR Sprint Cup championships consecutively from 2006 through 2010. That makes him tough in anyone's book.
His toughness is demonstrated with smooth driving that makes him a contender to win at many tracks, especially intermediate ones where 40 of his 58 career wins have come.
Johnson has a mild public persona, but he can actually get pretty fired up over the radio in his race car. He also has a fun-loving personality that many fans of the sport don't see.
Chemistry with his team, led by crew chief Chad Knaus, has made them the tough contenders that they are. When things are going well for this group there may well be another title on the way.
Johnson has three wins so far and is fourth in the standings. Can you say six-time?
Kevin Harvick, driver of the No. 29 Budweiser Chevrolet for Richard Childress Racing, is a talented driver with his 18 Cup wins.
He was thrust into the ride that was formerly driven by the "Intimidator." After his tragic death in 2001, Harvick had much to live up to at RCR, but he became his own man.
Harvick can be tough on other drivers if his feathers get ruffled. He won't hesitate to retaliate if he feels he was wronged on the track.
This driver doesn't lead a lot of laps, but he can suddenly be in the lead pack when the checkered flag waves. This season has not been strong for him, but he remains in the top 10 at ninth place.
He may be nicknamed "Happy," but don't underestimate how tough he can be as a racer. He doesn't hold back if he has an opinion to express, especially about another driver.
Matt Kenseth is known as the driver of the No. 17 Ford for Roush Fenway Racing, but that will change in 2013 when he moves to a new team yet to be announced. It may be the Home Depot car at JGR.
Kenseth's toughness comes in the form of his smooth driving style and unemotional demeanor. He can be a threat to win more often than not.
He has one Cup title and 22 career wins. This season he has led the points and is currently ranked second in the standings with one win.
Kenseth has undeniable talent as a driver, but he is somewhat of a stealth driver who keeps his equipment clean for the most part despite mixing it up for the lead in many races.
It would be an interesting scenario to see Kenseth wheel the Home Depot car against home improvement rival Jimmie Johnson in the Lowe's Chevrolet.
Kyle Busch, driver of the No. 18 M&Ms Toyota for Joe Gibbs Racing, is a young, talented driver who is tough because anything less than a win is like a loss to him.
He can be hot-tempered and aggressive behind the wheel, but he will do what it takes to get to the front if he has a car capable of doing so.
Busch, 27, is very accomplished with 24 Sprint Cup wins and a plethora of wins in the second and third tier of NASCAR's National series. He is a Nationwide and NCWTS team owner as well.
The driver of the No. 18 isn't having the best of seasons with his one win and inability to secure his place is the top 10 of the standings. He is fighting for the wild-card slot at this point.
Though Busch has mellowed this season, he is a threatening driver on the track and his desire to win makes him one tough contender.
Mark Martin drives a partial schedule for Michael Waltrip Racing behind the wheel of the No. 55 Aaron's Dream Machine Toyota.
Martin, 53, may have cut back his schedule a bit, but he epitomizes toughness with his mentality as a driver, his physical conditioning and continuing ability to qualify well and contend for wins.
He has 40 Cup series wins and is known for coming in second, not only in races, but in the run for championships as well.
Kurt Busch has been his own worst enemy by losing control of his emotions. It has caused him to fall from grace with top-tier teams like Roush Racing and Penske Racing.
The driver with one Cup title and 24 career wins now finds himself driving for a small team, Phoenix Racing. He pilots the No. 51 Chevrolet with Hendrick Motorsports' engines and chassis.
Busch can probably do more with less than any driver in the series. He is a very tough racer, but his equipment with the underfunded team hampers his ability to win races and finish well.
This driver is hardly a fan-favorite because of his emotional and inappropriate behavior displayed at racing venues. He is an intense driver who wants to win races and knows that he can.
It is likely Busch will return to a formidable team in 2013 if sponsorship is secured. Should he once again have a consistent, fast car, look for him to be a very tough contender to win races.