John Clayton, whose list of contacts in the NFL was matched only by his attention to detail and dedication to his craft, died Friday in Washington after a brief illness, his family said.

He was 67.

Clayton, nicknamed "The Professor," was one of the country's foremost NFL insiders in a five-decade career that included over 20 years with ESPN. Clayton's pursuit of news and information was done with such fervor that, as ESPN's Chris Mortensen said, "Anyone paying attention walked away a little more educated.''

"Long before he became an ESPN icon, John might have been the best news-breaking team beat reporter of his generation, the type who could sit on a story for months and then break it before others had any clue what was going on,'' said The Athletic's Mike Sando, a longtime friend of Clayton's. "He was that good. On a personal level, John was incredibly generous to me when I succeeded him as the Seahawks beat reporter at the Tacoma News Tribune many years ago. I owe so much to John and will miss him terribly.''

Clayton, a native of Braddock, Pennsylvania, began his career in 1972 as a teenager covering the Pittsburgh Steelers in a season that included the "Immaculate Reception.'' He continued his work up until just 10 days ago, when he broke down the Seattle Seahawks' blockbuster trade of Russell Wilson to the Denver Broncos for Seattle Sports 710 AM, where he was a regular contributor.

"We will all miss your words and brilliance @JohnClaytonNFL #RIPJohnClayton," Wilson wrote in a tweet, as he and former colleagues and friends of Clayton took to social media Friday night to offer remembrances.

"The Seahawks are heartbroken to learn of the passing of John Clayton," the team said in a statement. The Steelers called Clayton "a Pittsburgh media icon."

"The number of NFL execs and coaches that I've heard from have expressed an overwhelming theme of great respect and a sense of deep loss and shock,'' said Mortensen.

Clayton spent over a decade at the Tacoma (Wash.) News Tribune before a more than 20-year run at ESPN. Clayton also wrote for several outlets, including the Washington Post, in recent years after his long stint at ESPN, and had been the sideline reporter for the Seahawks radio network for five seasons. He also contributed stories for KKFN-FM (104.3 FM) in Denver since February of last year.

"John was a pioneer as an NFL insider but also one of the kindest men you could ever work with,'' said Seth Markman, vice president and executive producer at ESPN. "He literally never said no to a show that asked him to come on -- from 6 a.m. to midnight, if you asked for the Professor, he was there for you. I'll also personally remember how he loved and cared for his beloved wife Pat as she has battled multiple sclerosis. We will all miss John greatly.''

Clayton received the profession's highest honor, now known as the Bill Nunn Memorial Award, in 2007. The award is presented annually by the Pro Football Writers of America in recognition of "long and distinguished reporting in the field of pro football.''

"It's the highest honor any writer covering this sport can receive,'' Clayton said at the time.

"The PFWA mourns the passing of John Clayton. John was the PFWA's 19th president (1999-2000) and the organization's 2007 Bill Nunn Jr. Award recipient," the organization said in a statement. "'The Professor' was a friend to so many in our business. Our condolences to his wife Pat, family, colleagues and his many friends."

Clayton was also a longtime member of the Board of Selectors for the Pro Football Hall of Fame.

ESPN hired Clayton in 1995 as a jack-of-all-trades for its NFL coverage. SportsCenter producers created a weekly segment called "Four Downs'' pitting Clayton against NFL analyst and former quarterback Sean Salisbury. It became must-see TV.

As did his appearance on "This is SportsCenter" commercials for ESPN, which to this day are among the best of the popular segments. Clayton's appearance included a spot where he appeared as he would on SportsCenter, in a coat and tie, before he tore both off to reveal a Slayer T-shirt, let down his long hair, jumped on a bed and shouted, "Hey ma, I'm done with my segment.''

Clayton began his distinguished reporting career while still in high school, as he covered the Steelers. He attended Duquesne University and was hired by the Pittsburgh Press when he was a senior at Duquesne.

His love for football never wavered from those early days.

"Until they plant me, I guess," he told the Pittsburgh Post Gazette in 2018, when asked how long he would keep covering the NFL. "I love this stuff. What I love about it is there's so much more stuff we didn't have access to years ago and now we do -- the salary information, NFL Game Rewind where you can watch coaches tape. There's so much information and analytical stuff, it's phenomenal.''

Clayton is survived by his wife, Pat, and sister, Amy.