Chapter 3 of The Great Gatsby describes the first of Gatsby's parties that Nick attends. Nick narrates how he was sitting at a table with another couple while he was with Jordan Baker. The man at the table with Nick thinks he knows Nick from the army, and they start talking about their experiences in France:
We talked for a moment about some wet, gray little villages in France. Evidently he lived in this vicinity, for he told me that he had just bought a hydroplane, and was going to try it out in the morning.
Nick says he was just on the point of asking this stranger for his name when Jordan interrupts him. Then he tells the man that he has not even met Gatsby yet: "I haven’t even seen the host." It is then that the stranger reveals himself as Jay Gatsby, saying, "I’m Gatsby, ... I thought you knew, old sport. I'm afraid I'm not a very good host." Thus it is only by accident that Gatsby introduces himself and Nick comes to realize who Gatsby is.