Casper is a happy and pleasant ghost that depending on the media can be found in the cemetery or a haunted house. Despite being a ghost he likes to make friends with people.
Originating in the Noveltoon “The Friendly Ghost” he eventually became the subject of comics by Harvey Comics who eventually purchased the character outright.
In 1984 Harvey Comics sued Columbia Pictures for the Ghostbusters logo, feeling like it looked too much like Fatso, a side character of their Casper comics. The judge found that they had failed to renew copyright and therefore Fatso was public domain. Later research found this to be the case for Casper as well.
Notes
Dreamworks owns the trademark for “Casper, the Friendly Ghost” through its Classics Media subsidiary. Therefore any media using Casper can not be advertised under that moniker, but still can be freely used if trademark is respected.