Knickerbocker is, according to the introduction, the historian who first collected the story of Rip Van Winkle's improbable nap as part of his history of early Dutch colonial life in New York state. The introduction presents him as someone whose work is characterized by its "scrupulous accuracy," even though Knickerbocker is a fictional character generated by the author, Irving. That this absurd story, told by a man who does not exist, could be considered in any way accurate lends humor to the tale. 

Knickerbocker appears elsewhere in Irving's body of work, most notably in "The Legend of Sleepy Hollow." He serves as a kind of connective figure between that story and “Rip Van Winkle.” Both stories are like folktales in that the narratives are generally regarded as authorless. By inserting a fictional go-between, Irving can write these stories with magical and fantastic elements, all while imbuing them with artificial age and portraying them as having been "collected" and "presented" by someone else. By putting the story in the hands of a fictional historian and characterizing it as having been passed down from generation to generation, Irving creates a certain plausible deniability for himself while simultaneously allowing for a sharp commentary on the idea of truth. The entire idea of history is, in some ways, just another folktale.