Cortana is named after an imaginarily virtual character in the famous video game "Halo", it even sounds alot like her, and seems to have been engineered with a sprinkle of comedic chops.
Apart from intimating wittiness, Cortana also managed to conduct convincing impression on real world personal assistants. It could process through complex grammar and perform various tasks like facilitating of restaurant reservations and notifying you when the new appointments are in conflict with the previously scheduled meetings.
But, Cortana is still in its beta form and will be available soon in the United States. Further, it will be launched in China as well as UK during the second half of this year (2014). Rest of the world would have the privilege of using Cortana not before 2015.