Roy Williams, who restored the sheen to North Carolina basketball — and cut a sideline figure as a dapper dresser with a folksy charm — announced his retirement on Thursday, saying that he felt like he was no longer “the right man for the job.”

Williams, 70, is the third-winningest men’s basketball coach with 903 wins over the last 33 seasons at Kansas and North Carolina, where he won three national titles, the most recent one coming four years ago with a victory over Gonzaga.

His teams at North Carolina over the last 18 years had typically been offensive juggernauts, whose defining characteristic was a raft of skilled players with N.B.A. ambitions relentlessly attacking the offensive boards. The Tar Heels under Williams upheld the standard his coaching mentor, Dean Smith, had established — a worthy rival to nearby powerhouse, Duke, in what has for decades been college basketball’s most watched rivalry.

As his hair turned silver, Williams nevertheless was a haberdasher’s ideal on the bench, where his Carolina blue sport coats, ties and slacks conveyed a message he was once told: dress like you’re going to a job interview.

So it was a sign of the times, when college basketball was played in the pandemic, that Williams joined other coaches in the Atlantic Coast Conference in dressing down, agreeing to wear nothing fancier than polo shirts.

This season wore on Williams, who cajoled a young but talented team to recover from an unsteady start to reach the N.C.A.A. tournament. But the Tar Heels were blitzed in the opening game by Wisconsin, 85-62. Remarkably, it was the first time in 30 tries that his teams had lost an opening game in the N.C.A.A. tournament.

He lamented afterward that his freshmen had never had the chance to run through the tunnel at the start of a game and hear the roar of 21,750 fans at the Dean Smith Center.

It was one of several clues that he might be near the end.

“I started the season when I was 70 years old. I feel like I’m 103 right now,” Williams said after the defeat. “So that’s the first thing that’s happened. It has been a trying year. It has been a year that, 2020 and the first part of 2021, I haven’t enjoyed that much. It’s been a lot of stresses.”

During an emotional news conference on the Roy Williams Court in Chapel Hill on Thursday, Williams said that the results of the last two seasons had persuaded him that it was his time to go. His coaching, he suggested, had not been as sharp, and left his teams underperforming, especially in the final seconds of close games.

“I just didn’t get it done consistently enough,” said Williams, who added that he was “scared to death of the next phase.”

Williams’ retirement is the first of what could be a wave of Hall of Fame coaches exiting in the coming years. Syracuse’s Jim Boeheim is 76 and Duke’s Mike Krzyzewski is 72, the only men’s coaches who have won more than Williams. Rick Pitino is 68 and Tom Izzo is 66. Leonard Hamilton, who is on the Hall of Fame ballot this year, is 72. And Kelvin Sampson, whose Houston Cougars are in the Final Four, is 65.

The only hint of scandal during Williams’ career came when an academic fraud scheme, in which athletes were directed to sham classes, was uncovered. Williams was adamant that he did not know about the scam, bristling at the suggestion that he should have known.

It was also a sign that below his charming veneer he was fiercely competitive, just as it was when he would jump into a crouch — his face North Carolina State red — and shake his fists to exhort his team on.

“In today’s times, I should say that I’m not retiring or resigning — I’m opting out,” Williams said Thursday. “That’s the most ridiculous phrase I’ve ever heard in my life. Why the hell don’t you just say ‘I quit’?”

Williams, grew up in Asheville, N.C., and played on the freshman team at North Carolina. He asked Coach Dean Smith the next year if he could sit in the bleachers and take notes while the Tar Heels practiced. He got his start coaching high school basketball (and golf) in Black Mountain, N.C., and after five years Smith offered him a job as an assistant.

His most consequential contribution was recruiting a sinewy guard who was not yet a household name: Michael Jordan.

Williams left after a decade by Smith’s side to take the job at Kansas in 1988. The Jayhawks had just won the national championship, but were about to be slapped with a tournament ban for recruiting violations under the previous coach, Larry Brown, who had left for the N.B.A.

Kansas became a perpetual national championship contender and did it with panache — a fast-breaking offense paired with a rugged defense that were melded through crisp, detailed practices that mirrored the discipline with which his teams played. He turned out plenty of dependable N.B.A. players, though with the exception of Paul Pierce, no superstars.

A sign of the respect he engendered as one of basketball’s best coaches came when Jerry West, the architect of two Lakers dynasties, tried to lure him to Los Angeles. But Williams remained in Kansas for 15 seasons. He reached four Final Fours — splitting a pair of meetings with North Carolina and Smith — but a championship was elusive. His final game at Kansas came in a loss to Syracuse in the 2003 title game.

By then North Carolina had quickly slipped into disrepair.

When Smith retired in 1997, his longtime assistant Bill Guthridge was appointed as a replacement. Three years later, after persistent criticism (and two Final Four appearances), Guthridge retired. Williams was the obvious candidate, but he could not bring himself to leave Kansas. The job went to another former Tar Heel — Matt Doherty, who created such a mess that Smith quietly pushed for his ouster in 2003 after two seasons.

The question of whether Williams would turn down Carolina again hung over the 2003 Final Four.

After Kansas was upset by Syracuse in the title game, the television reporter Bonnie Bernstein asked him if he was leaving. “I could give a (bleep) about North Carolina right now,” Williams said in a live interview.

It was an uncharacteristically foul word from Williams’ mouth.

If he wanted to color his language, he often dropped “dadgum” into a sentence in his Blue Ridge twang. He did this so frequently that he picked up a nickname: “Dadgum Roy.”

It didn’t take Williams long to restore North Carolina to its station among college basketball royalty. In his second season, with players recruited by Doherty, the Tar Heels won a national title. They won two more championships, in 2009 and 2017 — and came agonizingly close to another, losing to Villanova in 2016 on Kris Jenkins’s long 3-pointer at the buzzer.

It might have been the most heartbreaking defeat, but the last losses of a season always linger, Williams said after what turned out to be his final one, to Wisconsin in the N.C.A.A. tournament. He apologized when he joined a videoconference call for blowing his nose, reminding reporters that he can get emotional.

“Basketball can be the greatest game in the world,” Williams said. “But when you lose it’s like somebody reaches in and grabs your heart and shakes it right in front of you. Sort of taunts you a little bit. But coaching basketball, that’s pretty dadgum good.”