Hours after agreeing to become the 28th coach in the history of the Washington Redskins franchise and the eighth of Daniel Snyder’s 15-year reign as owner, Jay Gruden described the opportunity as a “once-in-a-lifetime deal.” At a news conference at the team’s headquarters in Ashburn, Gruden vowed Thursday to do everything possible to return the downtrodden franchise to its former glory.

But the 46-year-old, who has spent the past three seasons as offensive coordinator of the Cincinnati Bengals, admitted turning around a team that finished last in the NFC East this past season will not be easy.

“There’s a lot of work to do,” Gruden said. “When you’re 3-13, there’s not one particular player or reason. There’s a lot of reasons and a lot of things that need to be fixed, no question.”

He added, “I will do my best to make sure that I put a competitive football team on the field every day. Really, it’s not about me, though. It’s about the Washington Redskins. This is about the fans. This is about the workers at FedEx Field. This is about the players. This is about the coaches. This is about the commitment to being a consistently great franchise, and wanting to provide everybody with the proud sense that we’re going to come to work every day and do the best we can to put a great football team on the field, every day.”

After Mike Shanahan was fired Dec. 30 following 40 losses in his four seasons in Washington, Gruden was considered a favorite among the potential replacements. He was the sixth candidate interviewed by General Manager Bruce Allen and other team officials and one of 11 coaches the Redskins requested to interview.

Keith McMillan explains what the creative play-caller will bring to Washington. (Jayne Orenstein/The Washington Post)

Allen and Gruden worked together with the Tampa Bay Buccaneers from 2004 to 2008, but Allen insisted Gruden didn’t have an edge on the rest of the field, which included Seattle offensive coordinator Darrell Bevell, Carolina defensive coordinator Sean McDermott, Baltimore offensive coordinator Jim Caldwell and San Diego offensive coordinator Ken Whisenhunt among others.

But “three-quarters of the way” through Gruden’s interview Wednesday, after he had laid out his vision for the team, the Redskins’ decision-makers agreed they had found their man.

“We were looking for a new leader: someone to inspire our football team,” Allen continued. “It was more than just X’s and O’s. It was about finding the right person to build the team chemistry that we needed. We needed someone who would be a good teammate to the coaches, the organization and the players in the locker room, and through this search, we kept looking for that leader and teacher.”

After successful runs in the AFL and UFL, Gruden joined the Cincinnati Bengals’ staff as offensive coordinator in 2011 and developed that collection of young players into a top-10 unit this past season.

With Gruden’s help, Cincinnati reached the playoffs in each of the past three years — something just four other NFL teams have done. And Bengals quarterback Andy Dalton has developed into one of the league’s better passers, ranking seventh in passing yards and third in the NFL with 33 touchdown passes.

Gruden takes the reins of a team that has made the playoffs just four times in the past 15 years and hasn’t made back-to-back postseason appearances since 1991 and 1992. A key task for Gruden will be helping quarterback Robert Griffin III rebound from a tumultuous second season that followed his offensive rookie-of-the-year performance in 2012.

Gruden said he hadn’t studied film of Griffin intensely but is encouraged by what he has seen.

“I see a ton of talent,” he said. “I see a guy that can run. I see a guy that can maneuver in the pocket. I see accuracy. I see long-ball accuracy. I see toughness. I see a guy that wants to win. I see a strong leader. I see every trait that a quarterback has to have to be successful. I see Robert having all of those. Why wouldn’t you want to coach a guy like that?”

The deterioration of the relationship between Griffin and Shanahan was seen as a main cause for the Redskins’ failures this past season. But Gruden said any past drama on or off the field didn’t concern him.

“I don’t know what happened last year, he said. “I know interviewing with Dan Snyder and Bruce Allen and everybody here that the passion for excellence is there. All they want to do is win, and they’re going to provide me with every avenue to win. I don’t know what happened last year, and I don’t care about what happened last year. I care about next year and moving forward.”

While Allen fielded questions alongside Gruden, Snyder sat in the second row with his wife and Gruden’s wife and sons. None of the past six coaches hired by Snyder finished his stint with a winning record. Gruden received a five-year contract, uncommonly long for a first-year coach.

Among Gruden’s first tasks will be assembling his coaching staff. People with knowledge of the situation say tight ends coach Sean McVay will be promoted to offensive coordinator, and they expect defensive coordinator Jim Haslett and defensive backs coach Raheem Morris to remain in some capacity. Gruden has worked with Haslett, McVay and Morris in the past, and said “I know those guys know football.” But he didn’t publicly commit to any of them and estimated he has received roughly 350 text messages from coaches in the past 24 hours.

“I don’t think finding a great coach and coaching staff is going to be difficult,” he said. “It’s finding the right ones that fit what I want to do and what the players want to do.”

Evaluating and improving the roster will be a collective effort, Gruden and Allen said. Front office members Morocco Brown and Scott Campbell will evaluate pro and college prospects, respectively, with input from Gruden. Allen said he will make the final decisions.

Gruden said he has confidence in his abilities as a leader and coach, but that Allen’s and Snyder’s confidence and desire proved reassuring.

“I just have a firm belief everything they were saying and their passion for the team and the city, the fan base, is legitimate,” he said. “I’m a pretty good reader of people and I can tell when I’m being lied to and I could honestly tell you this: Dan Snyder and Bruce Allen have the fans’ best interests at heart and the players’ best interests at heart and all they want to do is field a winning team. They’re giving me an opportunity to take this team to a great level, and I’m going to do everything I can to prove them right.”