|First appearance:||May 15, 1986|
|Last appearance:||September 16, 1995|
Rosalyn also appeared for a short amount of time as Calvin's Swimming lessons instructor. She also has a boyfriend named Charlie. Calvin, on one occasion, picked up the phone on the same line while Charlie had called Rosalyn, and proceded to tell him to break up with her and said she was a "sadistic kid hater". Rosalyn's idea of effective babysitting is a 6:30 bedtime for Calvin, and she has little patience for his attempts to rebel against her. Calvin will often freak out whenever he hears that Rosalyn is going to be babysitting him, in one instance screaming in protest non-stop for an entire strip (prompting his Mom to say in the last panel, "For goodness' sake, Calvin! Take a breath before you pass out on the floor!"). Another instance is when Calvin asks his Dad to get out the magnum, or at least a "wooden stake and a mallet." In one strip, she orders Calvin to go in the house and to his room, only to receive the reply "Jawohl, mein Fuhrer!" and the Hitler salute. In the final Rosalyn story, however, the traditional war is averted by a game of Calvinball, in which Rosalyn proves to be a formidable player, and once again trumps Calvin with a clever move in the last panel. This display of extensive imagination showed her to be not entirely lost to the dull world of adulthood, and this trait allows her to sympathize with Calvin's needs and ultimately control him much better than his mother ever could, such as in the same storyline as above, in which she allows him to stay up half an hour past his bedtime, and plays Calvinball with him, two actions which Calvin's mom would be sure to avoid (ironically, on returning home, Calvin's parents refuse to believe that she was able to play a game with him, and assume she is making a joke). Occasionally, Calvin manages to gain the upper hand (or at least until his parents arrive) by tricking Rosalyn into precipitous situations, such as locking her out of the house so he and Hobbes can watch TV and eat cookies, or taking Rosalyn's science notes, which she needs to study for a test the next day, and locking himself and Hobbes in the bathroom and threatening to flush them down the toilet if she didn't give into his demands.
In nearly all the "Rosalyn stories", Rosalyn is shown demanding advance payment and raises in wage from Calvin's parents, supposedly because she needs the extra money to pay for college or for the hard work she puts in to control Calvin. (For exactly the same reason, she briefly appears as Calvin's swimming instructor.) They are reluctant to pay such exorbitant rates, but even more unwilling to have Calvin ruin their outings. Therefore, they always gave Rosalyn her raise.
In at least four stories, Rosalyn telephones her boyfriend, Charlie, to cancel prearranged meetings which she cannot fulfill. (Charlie remains as an unseen character). Calvin sometimes breaks in and urges Charlie to stop courting Rosalyn, asserting that Rosalyn is either sadistic or insane, or both.
Not only is Rosalyn Calvin's baby-sitter, she is also his swimming teacher.
Rosalyn's hair color
In the only appearance of Rosalyn in a Sunday strip, we see Rosalyn with blonde hair. However, in the tenth anniversary book, we see a brown haired Rosalyn in the characters section. Since Rosalyn's hair is not coloured, the intention of a dark hair colour can be dismissed.