Nature
Given that Casper is depicted as a ghostly, portly little boy, there is a controversy among fans and critics of the series as to whether or not he is a dead child. Early Casper cartoons seemed to suggest this, as they portrayed him residing beside a gravestone. Specifically, the short "There's Good Boos To-Night" featured Ferdie, a fox befriended by Casper, coming back from the dead as a ghost. Casper's death (as well as the reason why he became friendly) have been disputed since that time.
This somewhat macabre premise was later abandoned in favor of the idea that ghosts were merely a type of supernatural being, similar to ghouls, goblins, etc. He was thereafter portrayed with feet and shown to have ghostly parents and became slightly slimmer. In the 1960s and 1970s, the stock answer provided by Harvey Comics in response to those wondering how Casper died was that he was a ghost simply because his parents were already ghosts when they were married.
The 1995 feature film Casper, however, revived the notion that Casper was a deceased human and provided a brief account of his death. According to the film, Casper was a young adolescent who went sledding all day and died of pneumonia. The first direct-to-video film to follow the feature, Casper: A Spirited Beginning, showed Casper's early days as a ghost, not showing how he died and ignoring the story provided in the previous film, although it does explain how he became friendly.
Read more about this topic: Casper The Friendly Ghost