Prior to 2012, Thomas had been an enigma.
With great speed to take the top off a defense, rare leaping ability and a frame that allows him to outmuscle any cornerback and most safeties, the 6'3", 229-pounder is one of the most physically talented receivers in the game.
Despite his immense gifts, the third-year pro mixed moments of brilliance with too many mental lapses, leaving fans and analysts to wonder if the king-sized wideout would ever realize his potential.
After catching passes from Tim Tebow and Kyle Orton, a heavy dose of Peyton's passes has been the missing ingredient in concocting one of the league's most improved players.
In the pre-Manning era, Thomas served as a dangerous deep threat, but he never reeled in the number of passes that he has this season.
During his rookie year, Thomas recorded eight catches in his debut, but he failed to top three catches in any game the rest of the way.
Last year, he recorded at least five catches in just three of 13 games.
With Manning behind center, it's been a whole different story.
While Eric Decker and Brandon Stokley have certainly helped draw attention away solely from Thomas, the Manning-Thomas connection has developed into a lethal combination.
That's not to say the relationship didn't have a few bumps in the road.
Andrew Mason of Sporting News cautioned fans that the connection might take some time to develop, and for the most part he's been right.
Thomas tried to get on the same page as Manning in the preseason, but with little success.
However, the two have picked things up as the season's wore on, and it should come as no surprise that the healthier Manning has got, the more productive the relationship has been.
Through 12 games, Thomas has already recorded at least five receptions in eight games, proving himself to be a reliable target for No. 18.
Where do you rank Demaryius Thomas among the NFL's best receivers?
Unlike Tebow, Manning is a precise passer and an elite pre-snap manipulator.
His ability to read defenses, make quick decisions and get the ball out accurately and on time has helped transform Thomas from a potential threat to an every-down beast.
The two continue to form a devastating red-zone combination, as Manning's ability to put the ball in only a place where Thomas can make the play has been a nightmare for opposing defenses.
No one knows for sure how long Manning will stick around, but you can best be sure his No. 1 fan has to be his No. 1 wideout.