The strip revolves around a mischievous six-year-old boy named Calvin and his stuffed tiger, Hobbes.
Despite his poor grades in school, Calvin demonstrates his intelligence through a sophisticated vocabulary, philosophical mind and creative/artistic talent.
Watterson described Calvin as having "not much of a filter between his brain and his mouth", a "little too intelligent for his age", lacking in restraint and not yet having the experience to "know the things that you shouldn't do.
When a scene includes any other human, Hobbes appears as a stuffed animal, usually seated at an off-kilter angle with a blank facial expression.
The true nature of the character is never resolved, instead as Watterson describes, a 'grown-up' version of reality is juxtaposed against Calvin's, with the reader left to "decide which is truer".
Although Hobbes's humor stems from acting like a human, Watterson maintained Sprite's feline attitude.
[7] However, Watterson sometimes uses them to explore situations adults can relate to, such as the desire to enjoy leisure time as opposed to the need to work, or bad customer service and frustrations when grocery shopping.
For several strips, Calvin and Hobbes fade into the background as Mom and Dad reflect on the impact of the event.
[6] An outdoorsman, he enjoys bike rides and camping trips, sometimes in extreme weather, and insists that these activities, like Calvin's chores, "build character".
On the rare occasions when she is not reacting to Calvin's misbehavior, she seems to enjoy quiet activities, such as gardening and reading.
Early on in the strip, Watterson says, the parent characters were criticized by readers for being overly sarcastic and insufficiently patient, especially Calvin's father, who has several times reminded his wife that he at first wanted a dog instead of a son.
One example, which Watterson selected for reproduction in the Tenth Anniversary Book, features Calvin telling Hobbes describing his Grandfather's complaints about comic strips: newspapers print them too small, and now they look like Xeroxed talking heads.
In contrast to Calvin, she is polite and diligent in her studies, and her imagination usually seems mild-mannered and civilized, consisting of games such as playing "house" or having tea parties with her stuffed animals.
In one strip it's shown that Susie plays lacrosse, when she uses her stick to fling back a pinecone that Calvin tried to hit her with.
Her parents are referred to several times in the strip, but have not appeared other than one brief shot of her mother's legs while talking to Calvin.
In another strip, Calvin calls Susie for help with homework, and she teases him that he missed "the melodious sound of [her] voice".
Watterson commented that a few astute fans of the strip have correctly asked him if Miss Wormwood was named after the apprentice demon in C. S. Lewis' The Screwtape Letters.
Miss Wormwood is rarely sympathetic to the trouble Calvin has in school, and comes across as a rather strict and sour character.
Calvin apparently takes joy in being the reason why Miss Wormwood mixes different stress-related medications (she "drinks Maalox straight from the bottle") and heavily smokes cigarettes ("Rumor has it she's up to two packs a day, unfiltered.")
Rosalyn, the last of the significant recurring characters to appear, is a high school senior and the only babysitter able to tolerate Calvin's antics.
Introduced in an early strip, meant to only be a one-time character, Watterson found her ferocity and intimidation of Calvin surprising, and he brought her back periodically in increasingly elaborate story-lines.
Watterson described their relationship as "one-dimensional",[21] although in her final appearance Rosalyn agrees to play a game of Calvinball, and in so doing, becoming the only character in the strip, other than Hobbes, to truly engage with Calvin on his own terms.
The collection Revenge of the Baby-Sat took its name from a storyline in which Calvin steals her study notes and threatens to flush them down the toilet bowl.