Ozmodiar

Ozmodiar is a little green space alien that only Homer Simpson can see.

Behind the scenes
Ozmodiar was introduced in a special episode of The Simpsons, where narrator Troy McClure presents him as a new character that would appear in the next seasons of the show. This was actually a joke, but Ozmodiar did make a brief appearance in another episode, where he speaks to Bart and Lisa (in spite of the fact that he's supposed to be only seen by Homer) after Bart comments that cartoons don't need to make sense.

The character is a parody of The Great Gazoo, from The Flintstones.