But it turns out Charles Schulz, creator of enduringly popular characters such as Charlie Brown, Lucy and Snoopy, was telling us more about his personal life than we would have guessed.
Now relatives of a woman who had an affair with Schulz four decades ago are auctioning off his love letters to her. And the family of the cartoonist, who died in 2000 at age 77, is upset.
Tracey Claudius, who is said to be ill, was 25 and an avid Peanuts fan when she was introduced to the married, 48-year-old Schulz by a friend in March 1970. They soon began a two-year relationship and Schulz wrote letters professing his love to Claudius.
[ Related: Charlie Brown and Peanuts pals head to big-screen ]
A 2007 biography of Schulz suggested his marriage to Joyce Halverson was already shaky when he began his affair with Claudius. He and his wife divorced in 1972 after she learned of his relationship with Claudius. He remarried a year later, after Claudius reportedly turned him down twice, the AP reported.
Schulz's daughter, Amy Schulz Johnson, told Britain's MailOnline that Claudius was being "immature" in offering the letters for sale.
"Of course it's [the auction] not in good taste," she said. "People do a lot of terrible things and I guess that's going to be one of them. It shows the lack of character of a person."
The beloved cartoonist's son Craig Schulz added that no one informed the Schulz family about the impending sale.
"Nobody has made me aware of the auction," Schulz told MailOnline.
"I would assume that she needs some money, that's why she's doing it. I have no idea why someone would do something like that."
There are 44 letters, which include 22 original drawings of Schulz's most famous characters. Many are signed with Schulz's nickname "Sparky."
The drawings show Charlie Brown and Lucy as stand-ins for Schulz and Claudius, MailOnline reported. In one, Charlie Brown visits Lucy's psychiatric help stand and asks, "Do you think monogamy is possible for humans, given how we're wired?"
In another, Peppermint Patty falls asleep in class and wakes up shouting "Tracey! Tracey, I love you! Tracey, do you hear me, I love you?"
And another has Snoopy refusing to go back to his doghouse, shouting "This isn't my home! It's a prison, a prison built of lies!"
[ More Brew: Toronto man leaves corporate job to build LEGO models ]
MailOnline said author David Michaelis's 2007 book, Schulz and Peanuts: A Biography, matched up the love letters with Snoopy cartoons to show how the affair influenced his work.
For instance, in two letters to Claudius, Schulz writes that he must stop phoning her because his wife had found out about his long-distance calls.
Later, Snoopy laments how he's not allowed to "see that girl beagle" and Charlie Brown warns him: "You'd better start behaving yourself...and stop making those long-distance phone calls."
Schulz also wrote to Claudius that he adored how she was "buggable" and "huggable," terms Snoopy also used in the strip to describe himself.