Though not explicitly labeled an "anniversary" issue on the front, there's no doubt that 50 issues was a major landmark for a Silver Age Marvel series, and that this John Romita cover is one of the most iconic images in superhero comic books.
Another Romita cover, this one specifically using the words "anniversary issue" for the century mark.
Fifty issues later, Gil Kane illustrated Spidey in the wake of the original Clone Saga.
John Romita returned for the 200th issue cover, which also revisited the original Spider-Man bad guy: The burglar that killed Uncle Ben.
Romita's son, John Romita Jr., was on board for the cover (and interiors) of the "special normal-sized" issue #250.
The first "full" appearance on Venom, and still one of Todd McFarlane's most iconic Spider-Man images.
Another Image founder, Erik Larsen, drew the cover to #350.
Holograms may not translate all that well to computer screens, but Marvel went all-in for them with Spider-Man's 30th anniversary in 1992.
Including on other Spidey titles, like Spectacular Spider-Man #189..
... and Web of Spider-Man...
... the adjectiveless Spider-Man title, the newest of the four series running at that point.
Less than a year later came the 30th anniversary of Amazing Spider-Man the series, not the character featuring the "final confrontation" between Spider-Man and Venom.
The tombstone-flanked cover of Amazing Spider-Man #400 made no secret that someone died inside. (Nearly 20-year-old spoiler alert: It was Aunt May, but more than 10-year-old spoiler alert don't worry, it wasn't really her.)
J. Scott Campbell brought Spider-Man and Mary Jane plus lots of villains together for issue #500, which reclaimed the book's original numbering after a relaunch a few years back.
John Romita Jr. illustrated the cover of 2009's Amazing Spider-Man #600 and the bulk of the interiors. Thanks to the book now shipping multiple times a month, #700 is scheduled for December of this year, just three-and-a-half years after #600 (and also set to be primarily written by Dan Slott).
John Romita Sr. also got in on the #600 fun.
Beyond Amazing Spider-Man, the spinoff Spidey titles also have had fun with anniversary issues, like this one featuring Spider-Man, Black Cat, Kingpin and The Spot in battle on the number 100 itself.
Sal Buscema had a long run on Spectacular Spider-Man, and this issue depicted the temporary death of (another old spoiler coming up!) Harry Osborn, at this point under the Green Goblin mask.
Not every anniversary cover can boast that it has both Will O' the Wisp and Rocket Racer.
Spider-Armor: Still iconic, and still appearing at some point in most every Spider-Man video game.
Spider-Man #50 saw Spidey versus the Grim Hunter, Kraven's son.
This issue not only brought Norman Osborn back in action as the Green Goblin, but featured the thoroughly final death of Spidey clone Ben Reilly, who died by Goblin Glider impalement, and subsequently degenerated into dust. He's managed to remain deceased, though there are vocal fans still hoping for his return (just go to a Marvel convention panel and see).
This issue of Ultimate Spider-Man left little doubt what issue it was.
One hundred Mark Bagley Spideys for Ultimate Spider-Man #100.
Ultimate Spider-Man #150 celebrated not only a milestone issue, but also the 10th anniversary of the Brian Michael Bendis-written series.
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