Nine

The Number 9 Man was a cameo character appearing in the first and second production seasons of Futurama. He was used merely as an Easter Egg in crowd scenes. But much like the career chips and the professor's PJ-joke, he was slowly forgotten and did not appear in season 3 and 4.

Some believe the reason for his number was to indicate a caste system, where lower numbers were basically slaves, and higher numbers were of kingly status. Where nine is in this system is so far unknown.

However, according to the commentary of Bender's Big Score his truth will be revealed in Into the Wild, Green Yonder. Where he will also have a voiced act.