Surely you've heard the joke. You tell Siri, "Call me an ambulance" and Siri responds, "From now on, I'll call you, 'An Ambulance', Okay?" As Leanna Lofte points out in a great writeup over at the iPhone Blog, that this joke can actually be of practical use.
You can create a more friendly identity for yourself by telling Siri to call you by your nickname, or simply indulge your monomaniacal streak by instructing her to call you "Master" or "Emperor" or similar.
Siri does this by checking out two fields in your primary Contacts entry. The Nickname field takes priority. When you say "Call me 'Master,'
The Phonetic First Name and Phonetic Last Name fields have been around for quite a while in iOS and OS X. They help you pronounce people's names while calling them. For example, you might enter "Ser Hee Yo" for a contact named Sergio. Siri now uses those fields to override the default pronunciation of your name, as well as for any other contacts that have unusual name pronunciations.
You can add these fields in iOS by tapping Edit, scrolling down to Add Field, and then choosing one of the phonetic options.