After a breakout 2015 season for the Oakland Raiders, Khalil Mack is approaching that territory of being the one defensive player in the NFL you'd want to build a team around.

Of course, the Texans' J.J. Watt is still at or near the top of that list, and Broncos outside linebacker Von Miller is right here after leading the Broncos to a Super Bowl championship. But with 15 sacks in 2015, Mack had four more than Miller and was just 2.5 behind Watt. While sacks certainly aren't the only measure of a great player, nothing on the defensive side of the ball is more valuable than a guy who can wreak havoc and get after the quarterback.

That's what Mack proved to be in 2015, and it's why he's on his way to superstardom. And what's the most exciting part about all of that for Raiders fans?

Mack turned just 25 years old Monday.

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After spending five years in college at Buffalo, Mack didn't come into the league at as young of an age as Watt and Miller, both of whom are 26. But following a rookie season in which Mack was good but struggled at times to finish sacks, he's already one of the elite pass rushers in the league heading into Year 3. He finished behind only Watt in sacks this season, and the Rams' Aaron Donald was the only other second-year player to even hit double digits (11).

The sky is the limit for Mack, who couldn't be off to a much better start to his career. For comparison's sake, Howie Long is the Raiders' all-time leader in sacks with 84 in 13 seasons, and he had just 5.5 total in his first two years. On the flip side, Mack has 19 sacks now in two years, and at this rate it would take him less than nine full seasons to set the franchise record.

Chances are it won't take that long, though, assuming the Raiders can keep him in Oakland.

Mack has two years left on his rookie deal, but contract negotiations will begin well before he has a chance to hit free agency in 2018. Derek Carr appears to be the answer at quarterback and Amari Cooper has a chance to be special at receiver, but it's hard to argue against any Raiders player being more valuable than Mack. General manager Reggie McKenzie won't let there even be a chance of him getting away.

Because for as good as Mack has been before hitting 25, there's no telling how great he can be in the years to follow.

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