Wikisimpsons - The Simpsons Wiki
Everyone thought Ray didn't exist and that Homer was the only one who saw him. Ray makes an appearance in front of the townspeople after everyone thinks Homer is going crazy, proving he does exist and is not just a product of Homer's imagination. Ray Magini is an anagram for "imaginary". The Bartender at Knockers couldn't see him because of his eye patch, Flanders couldn't see him because he hid behind the chimney, and Bart couldn't see him because of a complicated set of circumstances, later explained by Stephen Hawking.
Ray is a roofer (although he doesn't seem to have received much education in roofing). He also sometimes stacks items in hardware stores.
 Behind the Laughter
Ray Magini is voiced by Ray Romano and was designed to look and talk like him.