The NFL is a passing league. You know this. I know this. Just about everyone in the league knows this. 

Because it's a passing league, quarterbacks are the most important players on the field. And just about every quarterback has that one pass-catcher he trusts more than anybody else -- the guy he wants to go to in key spots, with the game on the line. With that in mind, we're going to use this space over the next several weeks to dig into some of the league's best passing-game combinations and what makes them tick. 

We're beginning today with Dak Prescott and Amari Cooper of the Dallas Cowboys

What defines Prescott and Cooper more than anything else is how they have each elevated each other's games during their time together. Prescott was a fourth-round pick who was thrust into spot-starter duty and performed well enough that the Cowboys had to bench their all-time leading passer, but he was in a pretty bad funk before Cooper arrived midway through last season. Cooper was a No. 4 overall pick who was considered one of the best receiver prospects in years and a Pro Bowler in each of his first two NFL seasons, but he was also in a pretty bad funk before being shipped off to Dallas midway through last season. 

In the 18 games they have played together, though, both Prescott and Cooper have been among the league's best players at their respective positions. Since Cooper's arrival, Prescott has completed 69.8 percent of his passes and averaged 8.2 yards per attempt while throwing 32 touchdowns against 13 interceptions. Cooper, meanwhile, has been on the receiving end of 106 passes, which he's turned into 1,573 yards and 13 scores. 

Compare their performance as a duo to what they did before being paired up, and it's not even close, for either of them: 

Prescott

Pre-Coop (39)

With Coop (18)

Cooper

Pre-Dak (52)

With Dak (18)

Comp

747

446

Rec

225

106

Att

1155

639

Tgt

389

147

Comp %

64.7%

69.8%

Rec %

57.8%

72.1%

Yards

8408

5245

Yards

3183

1573

YPA

7.3

8.2

Yds/Rec

14.1

14.8

TD

53

32

Yds/Tgt

8.2

10.7

INT

21

13

TD

19

13

Rtg

94.0

102.7

Rtg

87.8

127.7

What they have unlocked in each other, more than anything else, is the deep ball. In Oakland, 15.2 percent of Cooper's targets were thrown 20 or more yards downfield, according to Pro Football Focus. In Dallas, that number has been 19.0 percent. He caught just 45.8 percent of those deep passes with the Raiders, but with the Cowboys he's caught 60.7 percent of them. He had 11 touchdowns on deep passes in 52 games with Oakland, and he already has seven in 18 games with Dallas. 

Before Cooper's arrival, only 9.4 percent of Prescott's passes were thrown at least 20 yards downfield. Since Cooper's arrival, that number is 12.2 percent. Dak completed 38.0 percent of his deep balls before Cooper got to Dallas, but as mentioned, he's connected on 60.7 percent of his deep throws to Amari. He had just 12 touchdown passes on throws 20 or more yards downfield in his first 39 games, and he has seven to Cooper alone in the past 18. 

During his spectacular, three-touchdown game in an overtime win against the division rival Eagles last season, Cooper put on a show against the Philadelphia secondary, aided in large part by his ability to create late separation on go routes down the sideline. 

One of the best pure route-runners in the NFL, Cooper is an absolute master of the double-move (he leads the league in both yards and touchdowns on double-moves this season, per Sports Info Solutions), and Prescott has incredible patience in letting Cooper's routes develop, hanging in the pocket, and delivering the ball downfield. They victimized Jaire Alexander with two double-moves in the same game earlier this season. Alexander looked helpless. 

The first touchdown of Cooper's Dallas career came on what could loosely be described as a double-move, as he pressed Titans cornerback Malcolm Butler to the inside near the goal line before suddenly snapping off his route and pivoting back toward the front corner of the end zone. Earlier this season, at essentially the exact same spot on the field, the Cowboys went back to the exact same route and saw Cooper smoke Xavien Howard (who last offseason became the highest-paid corner in the NFL) for another score. 

The key to these routes is the footwork, which Cooper sells as well as anybody in the NFL. He really makes these cornerbacks think he's going one way, when really he's going another. Prescott, obviously, knows exactly where he's headed, and has a knack for perfectly placing the ball where Cooper is going to be, rather than where he is. All of this was on display back in Week 1, when Cooper gave poor Deandre Baker a ridiculously rude welcome to the NFL. Watch the clip below, and pay attention to how he hop-skips his way into a pitter-patter step within two yards of the line of scrimmage, then violently Euro-steps around Baker and heads for the end zone. Then, check out the ball placement from Dak, who couldn't throw a more perfect pass if he had 1,000 tries. 

As if elite route-running and separation ability weren't enough, Cooper also has the ability to explode for big gains after the catch. Whether he gets hit in stride or has to throttle down in order to make the grab, Cooper has shown that he can make guys miss in open space, accelerate away from defenders, and hit the jets to find his way to the end zone. 

The final piece of the puzzle for Cooper is his body control. He has an innate ability to maintain balance and composure while making contested catches, and he has incredible awareness of exactly where he is on the field. This makes him one of the best guys in the NFL at working the sideline and the back of the end zone, where he gets up on his tiptoes and hauls in throws that look like sure incompletions. 

If you go back through all six of those videos above, one thing you'll notice is that just about every throw hits Cooper right in stride, or directly between his shoulders. Cooper has struggled throughout his career with drops, and while he is excellent at a great many things, he does not have the world's widest catch radius. (Go check out the dropped pass that turned into an interception against the Packers earlier this season.) 

That's why it helps that Prescott has become one of the most accurate quarterbacks in the NFL. He currently ranks second in the NFL in Completion Percentage Above Expectation, per NFL.com's Next Gen Stats, completing 7.1 percent more of his passes than one would expect based on numerous factors such as receiver separation from the nearest defender, where the receiver is on the field, the separation the passer had at time of throw from the nearest pass rusher, and more. That's the fifth-best mark of any player during the Next Gen Stats era, which covers the past four seasons. (Prescott's 7.3 percent mark during his rookie season back in 2016 ranks fourth.) 

Prescott has been an efficient quarterback for most of his career, but now that he's marrying that efficiency with far greater volume, he is performing like one of the league's best players, making the snickers about his reported contract demands this past off season look silly. He leads the NFL in QBR, and ranks second behind only Patrick Mahomes in Football Outsiders' DYAR and DVOA. And considering he adds a ton of value with his legs as one of the NFL's premier non-Lamar Jackson rushing quarterbacks, it's likely that he's an even more valuable player than he appears on the surface. 

The Cowboys have maintained since the offseason that they fully intend to pay both Prescott and Cooper. Both players decided not to sign the deals they were offered over the summer, preferring instead to bet on themselves, wait out the market, and hope they could make themselves some additional money. It's safe to say they both made smart decisions.