Sal Paolantonio and Mike Reiss react to Rob Gronkowski's retirement, with Reiss saying it's a shock to the Patriots. (0:54)

Rob Gronkowski announced his retirement from the NFL via an Instagram post on Sunday. After nine seasons with the New England Patriots, he is putting an end to a career in which he transcended the tight end position and was one of the league's most colorful personalities.

Patriots quarterback Tom Brady shared his reaction in an Instagram post.

Gronkowski called Patriots owner Robert Kraft on Sunday to inform him of his decision to retire, a team source said.

"In the nine years that I have known Rob Gronkowski, I have never known him to have a bad day," Kraft said in a statement later Sunday. "He always has a youthful exuberance about him and is a joy to be around. As a player, he earned the respect of his coaches and teammates for his hard work, preparation, selfless attitude and the sheer dominance of his game. 'Gronk' quickly became a fan favorite and the most dominant player at his position for nearly a decade. I look forward to honoring him in the near future as both a Patriots and Pro Football Hall of Famer. "

Coach Bill Belichick said it was his "pleasure and a privilege to coach" Gronkowski in their nine years together, and credited him as a major reason the Patriots won championships.

"Rob's impact on our team and organization was felt in many ways," Belichick said in his statement. "In the ultimate team sport, Rob was a great, great teammate. His production spoke for itself, but his daily attitude, unmistakably positive energy wherever he went and toward whoever he touched will never be forgotten. Rob will leave an indelible mark on the Patriots organization and the game as among the best, most complete players at his position to ever play."

Gronkowski's 79 touchdown receptions since he joined the Patriots as a second-round draft choice in 2010 led the NFL. He had 10 or more touchdown receptions in five seasons, which is the most by a tight end in NFL history.

Gronkowski played in 115 regular-season games, totaling 521 receptions for 7,861 yards. He played in 16 playoff games, with 81 receptions for 1,163 yards and 12 touchdowns -- all records for a tight end.

Gronkowski's 12 postseason touchdown receptions are tied for second in NFL history among all players, behind Jerry Rice (22). He has four career 100-yard receiving games in the playoffs, tying him with Vernon Davis and Keith Jackson for the most by a tight end.

An often overlooked part of Gronkowski's game was his powerful blocking, which made him a rarity in today's game: a true "combination" tight end, equally effective as a blocker and pass-catcher.

In the days leading up to the Patriots' victory against the Los Angeles Rams in Super Bowl LIII, Gronkowski discussed the physical toll football had taken on him.

"The season is a grind. It's up and down. I'm not going to lie and sit here and say every week is the best. Not at all. You go up. You go down. You can take some serious hits," he said. "Try to imagine getting hit all the time and trying to be where you want to be every day in life. It's tough. It's difficult. To take hits to the thigh, to take hits to your head, abusing your body, isn't what your brain wants. When your body is abused, it can bring down your mood. You have to be able to deal with that, too, throughout the season. You have to be able to deal with that going into games."

play 1:42 Schefter: Injuries took their toll on Gronk's body Adam Schefter says Rob Gronkowski's injuries took a toll on his body, and he wanted to enter the next phase of his life.

The 6-foot-6, 268-pound Gronkowski has a lengthy injury history but has taken pride in bouncing back from various ailments, which have included surgeries on his back, forearm and knee.

Gronkowski, who turns 30 on May 14, was reflective at times leading into Super Bowl LIII.

"I'm really satisfied with how my whole career has been. Super satisfied. There's ups and downs, but the thing is always coming back," he said. "There's so many examples of great players here before me, when I was young, to look up to and see how they bounce back when something adverse comes their way."

Gronkowski's upbeat personality was infectious among his teammates, something that in some ways began the day the Patriots selected him with the 42nd overall pick out of Arizona.

"There was, like, a big mosh pit on stage, and I think everybody was excited to see that," Brady recalled in the days leading up to Super Bowl LIII. "I remember [receiver] Wes [Welker] being like, 'We got this guy, and this is the kind of attitude we need.' Gronk has cut it loose. I think everyone appreciates him."

At the same time, Brady highlighted a different side of Gronkowski, as he has long been one of the most philanthropic players on the team. In 2016, Gronkowski was the team's recipient of the Ron Burton Community Service Award.

"For as big and physical as he is, he is a gentle, kind man," Brady said.

Gronkowski's notable accomplishments on the field include: