The NFL's best, most intense, most fascinating rivalry didn't amount to much three years ago.

But what the San Francisco 49ers and Seattle Seahawks lack in history, they've more than made up for with their passion -- both on and off the field.

It's one of the most unique rivalries the league has ever seen, since it extends from the fan bases to the players to the front offices -- and, more than anything, to coaches Jim Harbaugh and Pete Carroll.

The teams' fans have gotten into the spirit of the Seattle-San Francisco rivalry. Steve Dykes/Getty Images

It all started when they were rival college coaches, with their infamous "What's your deal?" exchange at midfield after Harbaugh's Stanford Cardinal ran up the score on Carroll's USC Trojans in 2009. Since then, various amounts of fuel have been poured onto the flames, with moments such as Harbaugh's taking a subtle shot this past summer at the Seahawks' string of PED suspensions – and prompting Seattle players Brandon Browner and Golden Tate to fire back with how much they wish they could enact some physical revenge on Harbaugh if they ever got to line up against him on the field.

But more than anything, this rivalry has earned top billing because of how darn good these teams have become.

These NFC West foes are the two best teams in the conference -- maybe the two best teams in all of the NFL -- and they're the only obstacles left in each other's path to the Super Bowl as they prepare for Sunday's NFC Championship Game.

"There's no love lost and there's no love found," Seattle cornerback Richard Sherman said in his typical loquacious manner this week, not shying away from the storyline that has dominated both teams' camps.

But while Sherman has a tendency to take things over the top on occasion, you've got to give him credit for perfectly capturing the spirit of this surging rivalry this week.

"I don't hate anyone," Sherman said. "But passion, definitely. There'll be strong dislike. It's playoff football, so there'll be a lot of intensity anyway, even if we weren't two teams very familiar with each other. But there's going to be a lot of chippiness in a hard-fought game. The two best teams in the NFC are the ones that are here."

Sherman later added, "If we were both 4-12, it wouldn't be so intense."

The rivalry is probably as personal for Sherman as anyone else. He played under Harbaugh at Stanford, and Sherman's father, Kevin, once told Sports Illustrated that transferring from wide receiver to defensive back "saved" his son because he didn't have to interact with Harbaugh as much.