AMAZING SPIDER-MAN #50: Spider-Man No More
An instant classic. Lots of folks think it was Ditko, but this was all Jazzy John Romita.  The “Spider-Man quits” idea was a great one in this issue, but it was so popular that it became a trope.  Every three or four issues the cover would blare “Spidey Quits!” or “Spidey chickens out!” or some variation thereof.

It did get a little tiring.
amazing spider-man #51
This is also the first time Spider-Man put his hands on The Kingpin.  Kingpin started as kind of a gimmicky foe–with a gas-blowing tie pin and silly purple pinstriped pants with a white blazer.  Apparently, he couldn’t even afford a matching three-piece suit.

But the 1st appearance of The Kingpin1st appearance of The Kingpin was in issue #50, the famous “Spider-Man no more” issue.  Of course, we saw his back.  And that’s really the essence of the character–he doesn’t even need to turn to face people, ’cause he’s so damn badass.

These issue mark the first appearances of JJJ’s editor in chief, Robbie Robertson, although he’s just an unnamed black dude who smokes a pipe instead of a cigar.