From the study guide "Enlighten me! The Great Gatsby": he is a guest at
 Gatsby's party. While everyone else is caught up in the pursuit of 
wealth, fame, and experiences, the owl-eyed man seems to be the only one
 who "sees" the truth. He seems to represent the reader, in that he says
 what the reader is feeling. He questions whether Gatsby is for real, or
 just a facade. When Gatsby is killed, owl-eyes is the only former guest
 that attends the funeral. He seems to have true compassion for Gatsby 
and feels sorry for the man like the reader does by that point.