Jared Bednar.
Nathan MacKinnon didn't become a top 5 player in the NHL until Bednar got here and helped him calm down and stay even keel, rather than boiling hot all the time, and then getting down on himself when he didn't perform like he was capable.
Joe Sakic has made some really good secondary moves to improve the blue line and add depth, and along with Hepple and his staff made some good draft picks in Makar and Rantanen that are helping the team, but it's still being led by more or less the same core that's been here a little while now. Joe's been the same winner he's always been but that didn't turn this team into a consistent winning team until Bednar got here.
Landy is one of the best captains in the league (maybe even the best though I'm biased), but he was just as great a captain when they were losing. They just didn't have a good team, they didn't play a good two way game like they do now, and they didn't know how to win yet.
Bednar is the guy who is getting the absolute most out of almost every player. He's the guy who's helped Nate, Landy, Burakovsky, Donskoi, Bellemare etc have career years. He got great years out of guys like Comeau and Calvert.
I think he probably played a big role in helping Girard get through a really rough first half of the season, and help guide him to a great second half, instead of struggling all year. I think he probably helped Makar make a smooth transition in the NHL as well. Cale got better almost every game as he learned the details Bendar and Pratt were instilling in him.
He's the guy that seems to hit every pitch that's sent his way in terms of getting the most out of his players. The only exception is Zadorov where his tough love approach has backfired IMO.
This team plays a super confident, very detailed, two way game. It doesn't get overly emotional when the other team is playing overly physical or crossing the line. They don't ever seem like they can't come back in games. And the players are getting more skilled, more detail oriented, and just downright better each and every year under his tutelage.
He just never stops coaching. A lot of players would tune out his constant coaching on the bench in between shifts, but everyone seems to be very attentive when he speaks with them, and they all really seem to love playing for him.
Bednar has his flaws like his constant lineup changes, his overly critical approach with Z, and being too stubborn to make adjustments to his system, but I don't think any one person in the organization has played as big a role in turning this team into a Cup contender and creating the winning culture they have now as he has.