In no strip did Calvin ever say "God put me on this earth to accomplish a certain number of things. Right now I am so far behind that I will never die."
There is a fake strip◊ going around that has fooled a lot of people despite the font looking nothing like Watterson's handwriting, involving Calvin going on meds and Hobbes becoming just a stuffed tiger as a result.
The strip in which Calvin provides "Yakka foob mog. Grug pubbawup zink wattoom gazork. Chumble spuzz." as Newton's First Law "in his own words" inspired a comic book called Chumble Spuzz, by the artist of Axe Cop.
A decade after the series where Calvin and Hobbes traveled to Mars, NASA landed the Pathfinder probe on Mars. Scientists gave nicknames to the various rocks in the pictures that were sent back. Two of the rocks were called "Calvin" and "Hobbes".
Doing It for the Art: Watterson was notorious for resisting every attempt to have his creations merchandised. This has had a two-edged effect on fans, depriving them of many bits of memorabilia that they'd love to have but at the same time preventing possible commercial oversaturation that has happened to other famous comic strips. He also got into trouble with newspapers and syndicates for his strips, in particular his new Sunday strip layout. Usually, Sunday strips are 3 rows of panels. The first row contains the title, and usually a little panel that either contributes nothing or has its own "throwaway gag" that most newspapers remove, leaving the second two rows. He felt very constrained, and so he made use of the entire space with wild layouts of panels going all over the place, even having the entire thing be one panel, just so they'll be forced to run the whole strip.
Fanwork Ban: Watterson has been quite clear: NoCalvin and Hobbes merchandise, of any kind, EVER!
Infamously, neither he nor the syndicate have cracked down on the ubiquitous, unauthorized Calvin-peeing-on-things stickers in any effective way.
Keep Circulating the Tapes: Since Attack of the Deranged Mutant Killer Monster Snow Goons (the last strip compilation in the original "square" format) was never reprinted in a treasury, this is the only way to see the color versions of the Sunday strips between July 8, 1990 and April 10, 1991.
A strip from November 28, 1985◊, involving Calvin trying to bathe in a washing machine, only appeared in a few papers. It did not show up in any of the anthologies, which had an alternate strip (Calvin saying dinner tastes like bat barf, being told to go to his room, then ordering a pizza).
The original◊ version of the August 28, 1988 strip was unprinted for many years, as the books used a specially redrawn version◊ to fit the template of the books at the time. The original was eventually published in the Sunday Pages catalog.
Before adapting the character into one of Calvin's alter egos, Bill Watterson tried to produce a comic strip starring Spaceman Spiff. In this early version, Spiff was a cigar-smoking astronaut with a Chaplin moustache. He had a dimwitted assistant named Fargle, and they flew through space in a zeppelin. For obvious reasons, as Watterson notes in the Tenth Anniversary Book, the syndicates rejected it.
Watterson regrets introducing Calvin's uncle Max, who appeared in only one short storyline before being subsequently put back on a plane forever.
Reality Subtext: Countless strips were based on exchanges between Watterson and his syndicate.
Reclusive Artist: Watterson now paints landscapes and lives in suburban Cleveland, but he hasn't even been seen in public since 1995. The only piece of art that he has released since ending the strip was an oil painting sold to charity in 2011, and he's only heard from every 2 or 3 years, whenever he writes a very brief review of a book or gives a very brief interview. His audio-only appearance in the 2014 documentary Stripped (which he also drew the poster for) marked the first time his voice had ever been publicly recorded!
During his political cartooning years, he did the same, as well as skipping award presentations in his honor and ignoring the demands of his superiors, no matter how minor. This reclusive nature seems to point to a personal issue with people rather than concern for the well-being of his craft.
He resurfaced in June 2014, collaborating with Stephan Pastis of Pearls Before Swine on a short story arc.
Screwed by the Network: A variation. Universal Press Syndicate was happy to keep running Calvin And Hobbes, but their inflexibility in accommodating Watterson, especially with alternate strip layouts, was a major contributing factor to his decision to kill the strip.
Short-Lived Big Impact: Only had a run of 10 years, surprisingly short for such a successful comic strip, and absolutely no new strips or supplemental material (barring collections) have been made since—but it has still remained one of the most well-regarded, influential comic strips in the medium's entire history.
Shrug of God: Watterson's been very ambiguous with regards to Hobbes' true nature. He is real to Calvin, and a toy to everyone else, and which view is correct is entirely up to the reader.
Tribute to Fido: Hobbes was inspired by one of Bill Watterson's cats. He explains in the 10th Anniversary Book:
"Hobbes was very much inspired by one of our cats, a gray tabby named Sprite. Sprite not only provided the long body and facial characteristics for Hobbes, she was also the model for his personality. She was good-natured, intelligent, friendly, and enthusiastic in a sneaking-up-and-pouncing sort of way."
Chocolate-Frosted Sugar Bombs: Calvin's favorite breakfast cereal, of which he proudly eats multiple bowls a day (occasionally with cola instead of milk), even though it makes him hyperactive as a result.
Cool but Stupid: Indirectly, from the line "This is so cool!" "This is so stupid!"
Fuzz Therapy: How Calvin describes the mutual pleasure both he and Hobbes incur when he rubs the tiger's belly after a "rotten day".
Misery Builds Character: Often invoked by Calvin's Dad whenever he forces Calvin (or the family) to do something unpleasant. The line bellow is said by Calvin himself, parodying his own Dad. His mom nearly dies laughing. Dad scowls in reply, but admits that's pretty good.
"Calvin, go do something you hate! Being miserable builds character!"
Hobbes: Is Amazon Girl's super power the ability to squeeze that figure into that suit?
Calvin: Nah, they can all do that.
Noodle Incident: The mysterious "Noodle Incident". The story is just as fragmented and impenetrable in-universe; not even Santa Claus can piece it together. Calvin himself claims he was framed (on the few occasions he can even think about the event without having a panic attack). Word of God has said that he never actually went into detail about the Noodle Incident on purpose. Watterson had plans to before he ended the comic, but he then figured that no matter what he came up with, it would never be as hilarious as the many things that the readers could have thought about it.
What Could Have Been: Watterson wrestled, for many years, with the idea of creating an animated series of the strip. Although he rejected all other merchandising immediately, he has great respect for animation and considers it to have potential and possibilities that comics simply can't have. In the end, though, he decided against it; he was proud of the strip being his creation alone with no other hands involved, he found it scary to think of his characters being given voices (which would inevitably fail to match the ones in his or his readers' heads), and he decided that, regardless of animation's possibilities, Calvin was designed to be a comic strip and a comic strip only, and would inevitably lose something if adapted.