SANTA CLARA, Calif. — For nearly two decades, Peyton Manning has been the biggest of NFL stars.

Yet it still is almost unbelievable that Manning, a five-time MVP and future Hall of Famer, is here in Super Bowl 50 at all.

Manning has so often used the word “unique” to describe his 2015 season, but it’s so much more than that. It was unfamiliar and frustrating, challenging and humbling, and finally, it was exhilarating, to make it to his fourth Super Bowl after all of it.

“There is no question it’s important to me, it’s very personal to me, and no question this season has had some unique challenges. I try to stay in the moment, I try not to assume that this is how things are going to be from here on out,” Manning said. “I really even with all the different challenges I felt like peace about it the whole time. Not knowing how it was going to work out, I had a peace about it and that certainly helped.”

Manning’s 18-year NFL career might end here at Levi’s Stadium on Sunday in Super Bowl 50, and if it does, it would be a fitting finish for the future Hall of Famer, even if it’s an ending no one could have predicted a month ago, or really, at any point in 2015.

But will it end with Manning’s second Super Bowl ring, a championship that would vault him into elite quarterback company, or will it end with another disappointing postseason loss?

Those closest to him say it doesn’t matter, that Manning’s legacy is set regardless of the outcome of Super Bowl 50, because just getting here at the end of the most tumultuous year of his career has been the ultimate victory.

“He got another chance and took advantage of it. If that doesn’t summarize what he’s all about, I don’t know what does,” former Broncos and Colts wide receiver Brandon Stokley told USA TODAY Sports. “It should be a great teaching tool. With what he’s gone through this year, and how he’s persevered and just overcame so many things, and now he’s at the Super Bowl.”

Manning has admitted this week that this could be his final season, though he’s been reluctant to make anything that could be construed as a retirement decision while here in Santa Clara. But it has been clear he’s been enjoying this chance to reflect on everything it took to get here, from frequent references to his NFL quarterback father, Archie, and brother Eli.

“I’ve kind of stayed in the moment and looked at the task at hand. I’ll do that this week and then. At some point after the season, I’ll have that comprehensive analysis, but I’m really at peace with it. I’m at peace with what happens,” Manning said.

It was a year that began with uncertainty, with Manning literally limping away from Sports Authority Field at Mile High in January and into an uncertain future. His body had failed him late in 2014, and his team’s failure in the divisional round of the playoffs led to a regime change in Denver. With John Fox out and Gary Kubiak in, Manning had to decide not only if he could return for an 18th season at age 39, but if he could do it while learning a new offense.

The Broncos also asked him to take a pay cut — the first such request of his career — and they eventually agreed on a $4 million reduction, from $20 million to $16 million. The savings certainly helped with general manager John Elway’s free agency budget, but it was one of just many signs that the Broncos were rapidly becoming a team in which Manning was no longer the focus.

From a classic Kubiak offensive scheme that relied on the running game and ball control and required the quarterback to play from under center to a team laden with defensive stars, the 2015 Broncos looked nothing like any previous Manning team. And for the only time in his four Super Bowl appearances, his team is here in Super Bowl 50 not because of him, but in spite of him after a season in which threw 17 interceptions in his first nine starts and then missed the next six and a half games while recovering from a torn plantar fascia.

Those six weeks were among the most trying of his career, and his frustration with the first significant mid-season injury of his adult life was clear to those who saw him every day. Stokley, who lives in a suburb south of Denver, was among those who to keep Manning’s spirits up away from the Broncos’ training facility, while quarterbacks coach Greg Knapp was the one responsible for giving Manning to work through a long rehab process that included more than a week in a walking cast and a series of weeks in which he could not participate in practice.

“It would have been so easy for him to say, ‘I’m done. Put me on IR. The foot’s not how it should be, it’s not feeling good.’ Throw in the towel and call it a career, or at least call it a career,” Stokley said. “But he didn’t. He kept grinding.”

Perhaps it’s with the benefit of hindsight, but Knapp says now he always believed Manning would eventually wind up back in the Broncos’ huddle this year. But maybe it’s just that Knapp had to believe it so he could convince Manning to keep grinding through those early morning workouts with practice squad receiver Jordan Taylor, all while the Broncos were winning games without him.

“It was making sure to remind him of all the positive things he had done to help us get to this spot, because when he got hurt, we were still doing very well as a team,” Knapp told USA TODAY Sports. “It was definitely challenging off the field. But the communication we had built up already, it carried over.”

In the final weeks of December and into early January, Manning began working as the Broncos’ scout team quarterback and eventually, in Week 17, suited up as Brock Osweiler’s backup, something he hadn’t done since his freshman year at Tennessee, when he briefly served as the backup to Todd Helton.

If not for five quick turnovers in the first three and a half quarters of that game — a pair of fumbles by a running back and a wide receiver, and a fumble and two interceptions by Osweiler — Manning may never have returned to the field at all.

But the time away not only allowed Manning’s foot to heal and his right arm to rest, but it also gave him a new appreciation for the Broncos’ offense. When he returned, he did so with more snaps from under center, and without committing a turnover.

Call him a game manager now, and he won’t be offended. If the Broncos beat the Panthers on Sunday, Manning could wind up in the MVP, but the way the Broncos are built, he’s only one of a dozen potential candidates.

“I think Peyton just needs to be Peyton. I don’t think he needs to do anything extravagant or crazy,” tight end Owen Daniels said. “We’ve got to play well all around Peyton. That’s a big thing for us. If we play well all around him, we’re going to be just fine because we know he’s going to do his job. He’s going to put us in the right place in every situation. He’s going to manage stuff at the line of scrimmage. He doesn’t need to go out and be a superhero. We’ll help him out. It’s going to be a team effort like it has been all season for us.”

Though retirement speculation has fueled Super Bowl media week, the Broncos say they will put no pressure on Manning following Sunday’s game to make a decision. Perhaps that’s because Manning’s boss, general manager John Elway, understands the internal struggle Manning may be dealing with better than most. Elway ended his Hall of Fame career after leading the Broncos to their second consecutive title in January 1998.

If Manning wants to seek his counsel later, Elway will tell Manning to “relax and smell the roses.”

“It’s always a tough decision and always a personal decision,” Elway said. “He can talk to as many people as he wants but bottom line is ultimately he’s going to have to make that decision.”

Follow Lindsay H. Jones on Twitter @bylindsayhjones.