On Earth, his name is Harvey Sandman. He owns a mattress company and is known to the human world as The Mattress King. He hypnotizes people, such as Timmy's dad, into buying his mattresses despite the number they already have bought from him.
Every sleeping wish has to go through him, not a fairy godparent, since he is the fairy of sleep. And if people aren't getting enough sleep, he shrinks.
He's the one who loaned the Sleepmaster 5000 bed to Rip Van Winkle. That caused Van Winkle to sleep for 20 years.
He was voiced by Jackie Mason.
He shrinks if people do not get sleep. This is similar to Cupid, who needs people to express love to each other to keep him alive and his equipment and love army working, otherwise he will disappear along with love.
It is likely that he is Jewish because of his Yiddish accent, the pronounciation of his last name, and his love for Jewish foods like knishes.