Dwight Clark, who made one of the most famous catches in NFL history, died Monday -- 15 months after he announced he had been diagnosed with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease. He was 61.

Clark's wife, Kelly, announced his death on Twitter, saying that she had lost her "best friend and husband."

"He passed peacefully surrounded by many of the people he loved most," Kelly Clark wrote. "I am thankful for all of Dwight’s friends, teammates and 49ers fans who have sent their love during his battle with ALS."

"We extend our condolences and prayers to Dwight's wife, Kelly, his family, friends and fans, as we join together to mourn the death of one the most beloved figures in 49ers history," the organization said in a statement. "For almost four decades, he served as a charismatic ambassador for our team and the Bay Area. Dwight's personality and his sense of humor endeared him to everyone he came into contact with, even during his most trying times. The strength, perseverance and grace with which he battled ALS will long serve as an inspiration to so many. Dwight will always carry a special place in our hearts and his legacy will live on as we continue to battle this terrible disease."

A two-time Pro Bowler, Clark played for nine years with the San Francisco 49ers and became known as one of quarterback Joe Montana's most reliable receivers. But his career was defined by a play known simply as "The Catch."

With less than a minute to play in the 1981 NFC Championship Game, the 49ers trailed Dallas 27-21. Facing a third down at the Dallas 6, Montana rolled out to his right and lofted a pass that appeared to be sailing out of bounds.

Clark leaped up in the back of the end zone and hauled in the pass with his fingertips, giving the 49ers a 28-27 win and sending the franchise to its first-ever Super Bowl. Two weeks later, the 49ers won the first of their five championships by defeating the Cincinnati Bengals, 26-21.

"Start of a dynasty," said former 49ers president Carmen Policy. "I don't let myself go down the road of what would have happened if he doesn't make that catch? As Joe Montana says, what would have happened if I didn't throw that pinpoint pass perfectly angled to be in the only spot where he should catch and no one else would be able to interfere with it. But without that play, I wonder where we would have been. And I stopped thinking about it, because so much happened after that. And yet, Dwight seemed to handle it in stride and the two of them, The Butch Cassidy and the Sundance Kid, they used to have fun playing off of each other, or who would take the credit, and this and that and so forth. But it was a special day."

Clark made his second consecutive Pro Bowl in 1982, a strike-shortened season in which he caught 60 passes despite playing in just nine games. He added a second Super Bowl ring to his playing resume following the 1984 season when the 49ers defeated the Miami Dolphins, 38-16.

Clark retired after the 1987 season and got into the management side of football, becoming the 49ers general manager in 1998. The following year, Policy hired him to be the general manager and director of football operations for the reborn Cleveland Browns. Over Clark's three seasons in charge of player personnel, the Browns went a combined 12-36. Clark resigned prior to the 2002 season after head coach Butch Davis demanded control over personnel decisions.

In March 2017, Clark announced he had been diagnosed with ALS. In an open letter, he said he had been experiencing symptoms since 2015. By the time Clark went public with his diagnosis, he said he was no longer able to button his shirt.

"While I’m still trying to wrap my head around the challenge I will face with this disease over the coming years," Clark wrote, "the only thing I know is that I’m going to fight like hell and live every day to the fullest."

"My heart is broken," former 49ers owner Eddie DeBartolo Jr. said in a statement. "Today, I lost my little brother and one of my best friends. I cannot put into words how special Dwight was to me and to everyone his life touched. He was an amazing husband, father, grandfather, brother and a great friend and teammate. He showed tremendous courage and dignity in his battle with ALS and we hope there will soon be a cure for this horrendous disease. I will always remember Dwight the way he was -- larger than life, handsome, charismatic and the only one who could pull off wearing a fur coat at our Super Bowl parade. He was responsible for one of the most iconic plays in NFL history that began our run of Super Bowl championships, but to me, he will always be an extension of my family I love him and will miss him terribly."

Clark joined the Niners as a 10th round pick out of Clemson in 1979 in the same draft class that brought Joe Montana to San Francisco. He got there by good fortune after only 33 catches in three college seasons as former 49ers coach Bill Walsh needed someone to catch passes from Steve Fuller at a pre-draft workout.

Clark impressed Walsh enough to get drafted and eventually made the team.

"He's meant the world to me for so many years," Montana said last year after a street near the site of the Candlestick Park was named for him. "We came into the league together and we laugh about things that he did all the time. I don't think he ever unpacked. By his rookie year he always left the playbook on his bed just in case he ever got cut. He kept trying to tell me he was getting cut every day, I kept trying to tell him, 'what are you doing? You're crazy."'

Clark made his last public appearance in October when the 49ers hosted "Dwight Clark Day" at Levi's Stadium. Clark spoke to the crowd from a suite that afternoon in a weakened voice, calling his disease a "little thing" he was dealing with at the time. He also thanked the fans and dozens of teammates who came back for the event.

DeBartolo recently hosted a reunion in Montana where many of Clark's former teammates came for one final goodbye.

In addition to his wife, Clark is survived by three children, daughter Casey, and sons Riley and Mac, from a previous marriage.

The Associated Press contributed to this report.