If the character is important enough that readers should pay attention to him or her, refer to him or her by his or her most common nickname employed in dialogue or by his or her first or last name. Whatever you want him/her to be known as, in other words. This can be done either directly through text or indirectly through markers placed in the scene so the character knows he or she is being referred to. Readers understand immediately when a character's name is mentioned and they make their own assumptions based on previous knowledge of the character. For example, if I mention "Joe", you might guess that I'm talking about Joe the bartender because we've never met but have only spoken on the phone several times. If I had described him with some detail perhaps you would know that this was not Joe the bartender but rather some other Joe who looks just like him. In addition to a character's name, writers often use descriptors to further explain who someone is. These descriptors can be physical (e.g., "the man with two left hands") or personality traits (e.g., "a man who loves his daughter dearly"). Descriptors help readers understand who is involved in the conversation and they also provide information for future references to these people or events.