Ruben is a busboy at Melville's Restaurant.  He is an unseen character, and is comically referenced in several episodes beginning in Season 6. He is first mentioned in My Fair Clavin, and is described as "soft and sweet with a voice like a nightingale".

In Woody Interruptus he is described as distraught after breaking up with the pastry chef.  

In The Bar Manager, The Shrink, His Wife, and Her Lover, Ruben is revealed to be an undocumented illegal immigrant, and is accidentally shot in the foot by Louis Pascal.