For those not familiar with Xbox game Halo - Cortana is the Artificial Intelligence, voiced by Jen Taylor, that helps Master Chief in the Halog game series - More about Cortana from Halo here: Cortana - Wikipedia, the free encyclopedia - I still have to play Halo 4, it's been out probably a year and a half now! Back to the story.

Microsoft releasing Cortana for Windows Phone 8.1

you can set up a nick name for Cortana to call you, this is why I guess a lot of people will change it to Master Chief!

More about it on The Verge:
This is Cortana, Microsoft?s answer to Siri | The Verge

Microsoft’s upcoming Windows Phone 8.1 update will include Cortana, a personal digital assistant designed to rival Siri and Google Now. Sources familiar with Microsoft’s plans have revealed to The Verge how Cortana looks and operates, replacing the built-in Bing search functionality on Windows Phone 8.1.