The Lions revealed the news on their official website, and NFL on ESPN sent out the following tweet:
Bleacher Report also paid homage to one of the most productive receivers of his generation:
ESPN's Adam Schefter was the first to report Johnson's intentions in February.
While some assumed the initial report of Johnson's retirement was a power play for a trade or perhaps even more money, NFL Network's Andrew Siciliano pointed out that he was true to his word:
A player walking away while still in their prime often comes as a major shock to fans, but Pete Prisco of CBSSports.com sees it from Johnson's perspective:
The aptly nicknamed Megatron was arguably the most dominant pass-catcher of his time, earning six straight Pro Bowl nods and three first-team All-Pro selections to go along with 11,619 receiving yards and 83 touchdowns over the course of his illustrious career.
Per SportsCenter, that makes Johnson the most prolific pass-catcher in Lions history:
According to ESPN Stats & Info, only two wide receivers in NFL history were more productive than the Georgia Tech product in their first nine campaigns in terms of yardage:
That includes the single-season NFL record for receiving yards, which he set in 2012 with a remarkable 1,964 yards on 122 receptions.
He also has the most 100-yard receiving games in the NFL since Detroit selected him with the No. 2 overall pick in the 2007 NFL draft, per ESPN Stats & Info:
In addition to that, only New England Patriots tight end Rob Gronkowski has more touchdown receptions than Megatron over the past six seasons, per Mark Daniels of the Providence Journal:
Although Johnson was an absolute monster from a statistical perspective, his lack of playoff success gives him a dubious distinction, according to the Elias Sports Bureau, via ESPN Stats & Info:
San Francisco 49ers great Jerry Rice would likely beg to differ, but MurtinezPls on Twitter suggested Johnson is the greatest of all time:
Regardless of his place on the all-time list, Dan Katz of Barstool Sports Chicago accurately captured the feelings of Lions fans following Johnson's announcement:
With so much production and so many accolades to his credit, Johnson's decision to walk away at such a young age is somewhat perplexing and reminiscent of another Lions great—running back Barry Sanders.
Megatron did give fair warning, though, by announcing his intention to mull over his NFL future following the 2015 season in early January, according to Tim Twentyman of the Lions' official website: "Like many players at this stage of their career, I am currently evaluating options for my future. I would expect to have a decision regarding this matter in the not-too-distant future."
Jeopardy! Sports shared a humorous parody highlighting the frustration Johnson may have felt playing for a team that couldn't get it done in the postseason:
On the heels of that statement, ESPN's Ed Werder reported that sources informed him Johnson was considering retirement rather than attempting to force a trade elsewhere, per ESPN.com's Michael Rothstein.
Werder's source suggested the myriad injuries Megatron has suffered in recent seasons played a big role in his desire to step away:
I think that's the whole thing. I think Calvin [is] that kind of guy if I don't feel I'm into this 100 percent, then I need to think about if I want to be in it at all. ... This time of year, you could probably ask a lot of players that question, and their bodies would tell them they wouldn't want to play. I think he's tired. His body probably aches, and probably all of them do.
Although Johnson has missed just nine games in as many seasons, he has spent a considerable portion of the past couple of years playing at less than full strength. That was especially true in 2014, when he missed three contests and played in several others with a high-ankle sprain.
Megatron was among the most prolific receivers the NFL has ever seen when healthy, however, due to his combination of size, speed and strength, and ESPN's Matt Bowen believes he was a game-changer in that regard:
While it certainly seems as though Johnson has plenty left to give, he accomplished more in nine seasons than most players in lengthier careers.
Perhaps the only thing missing from Johnson's career resume is a playoff win, having fallen short in two postseason tilts.
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Johnson was part of many bad Lions teams during his time in the league, so the fact he was able to make the playoffs twice is a testament to just how dominant he was at the wide receiver position, frequently putting the offense on his back.
If Johnson's retirement is indeed permanent, the only question that remains is if he will one day have a bust in Canton, Ohio, as a member of the Pro Football Hall of Fame.
While Johnson isn't particularly high on the all-time receiving list due to his relatively short career, Siciliano is fairly confident there is a place for him in the Hall of Fame:
Peter Schrager of FoxSports.com agreed and put him in the same class as fellow retirees in Denver Broncos quarterback Peyton Manning and Oakland Raiders defensive back Charles Woodson:
Hall of Fame cornerback Deion Sanders intends to be present if and when that occurs:
Playing another few years almost certainly would've cemented his place among the sport's immortals, but even after playing only nine seasons, Johnson has an extremely strong case as the most formidable and productive receiver of his era.
Follow @MikeChiari on Twitter.