Beetlejuice is an evil spirit who acts as the protagonist villain of the live-action movie "Beetlejuice" as well as a more anti-heroic character in the cartoon series that followed.
In the movie, Beetlejuice was darker and more openly malicious than he would become in the cartoons, arguably being one of the main villains - though he also acted as a benefactor (of sorts) to the heroes: though there was no attempt to hide the fact that Beetlejuice was not meant to be a nice character, even the heroes that summoned him knew that he was, pretty much, a demon.
However, Beetlejuice was still used as a force of (relative) good as his chaos was directed largely at a group of human antagonists - though he was still rude, obnoxious, and hostile towards the heroes as well, not to mention the fact that he also tried to force one of the main heroes to be his unwilling bride - much to her disgust.
As mentioned before when the Beetlejuice cartoon came out they altered his personality somewhat and while still being an agent of chaos and a fairly macabre character he was more heroic than he had originally been portrayed in the film and even had a human friend (ironic considering in the original film he labelled himself a "bio-exorcist").
Beetlejuice was originally an assistant to Juno until he went rouge as a freelance bio exorcist. Until Juno banished him in a model cemetery. It wasn't long until he was released from his model prison and once again spread chaos.