Harriet Glickman, the Los Angeles teacher who inspired Peanuts creator Charles M. Schulz to introduce Franklin -- the beloved comic strip's first African-American character -- has passed away.

News of Glickman's passing was broken by the Peanuts-based website The AAUGH Blog. Author Nat Gertler, who knew Glickman personally, says her death was "peaceful, in her sleep" and that the former schoolteacher had been "well prepared for this."

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Glickman famously wrote a letter to Schulz on April 15, 1968 -- urging the cartoonist to add a Black character to Peanuts, describing the gentleness of the comic strip as "the perfect setting" for such representation. Following continued correspondence between Glickman and Schulz, the character of Franklin made his debut later that year on July 31. Franklin's last appearance in the comic strip came in 1999, one year before Schulz died at the age of 77.

Franklin has gone on to appear in various other pieces of Peanuts media, including the various television films and specials the comic strip spawned. Most recently, the character appeared in 2015's The Peanuts Movie, voiced by Marleik "Mar Mar" Walker -- who partook in promotional events alongside Glickman.

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In the years following Franklin's introduction, Schulz spoke candidly about response to the character. In a 1997 interview in particular, the cartoonist recalled an incident in which he received a letter from a southern editor who "said something about, 'I don't mind you having a black character, but please don't show them in school together.' Because I had shown Franklin sitting in front of Peppermint Patty." As far as how he handled the situation, Schulz said, "I didn't even answer him."

Glickman was born in 1926. She was 93 years old.