Paul Zimmerman, the longtime Sports Illustrated NFL writer known as "Dr. Z" for his analytical approach, died Thursday. He was 86.

NBC Sports football writer Peter King confirmed Zimmerman's death. King worked with Zimmerman at Sports Illustrated, and completed Zimmerman's autobiography, "Dr. Z: The Lost Memoirs of an Irreverent Football Writer."

Zimmerman had three strokes in 2008 that ended his writing career after 29 years as Sports Illustrated's lead pro football writer.

"When I started covering football in 1984, he was Peter Gammons and Bob Ryan and Tex Maule rolled into one," King said. "His football knowledge was peerless. He knew the technical side and loved it, and he loved the personal side too."

Zimmerman briefly played college football at Stanford and Columbia, and covered the New York Jets for the New York Post for 13 years. He also worked for the Sacramento Bee, New York Journal-American and the New York World-Telegram & Sun before joining SI in 1979. His "A Thinking Man's Guide to Pro Football" was published in 1970, and revised in 1984 as "The New Thinking Man's Guide to Pro Football."

New England Patriots coach Bill Belichick opened his news conference Friday by recognizing Zimmerman.

"Paul was a great ambassador for professional football, and I think that what he did through the years with his background and insight on the draft, I would say some of the behind-the-scenes organizational insight that he gave due to his great sources and trust that he created with so many people was pretty interesting reading in the Sports Illustrated columns," Belichick said. "I always kind of felt like Paul and Will McDonough were kind of two of the really well-connected, respected writers that covered the game, certainly when I came into the game and then for many years thereafter. So certainly a sad day to hear about his passing. He made a great contribution and certainly popularized a lot of things that today have blossomed into major, major stories and events that I'd say he was in there on the ground floor on."

Zimmerman was president of the Pro Football Writers of America during the 1982 season. He received the PFWA's highest honor, the Dick McCann Award, in 1996 for a long and distinguished contribution through coverage. In 2014, the PFWA instituted the Paul "Dr. Z" Zimmerman Award, given for lifetime achievement as an assistant coach in the NFL.

The Associated Press contributed to this report.