When you interact with Cortana, you're in touch with the work of Jonathan Foster's team. He leads creation of what Cortana says, which is a major part of how she shows her "personality".
Cortana, digital assistant with personality - https://community.windows.com/en-us/videos/cortana-a-digital-assistant-with-personality-and-smarts/cZo045p0J4Y
Cortana engineer Jason Deakins loves how Cortana saves the day, even over multiple devices - https://community.windows.com/en-us/videos/meet-jason-helping-cortana-save-the-day/FcLiBAHRyAs
Engineer Xin Zou brings a local experience to Windows and Cortana - https://community.windows.com/en-us/videos/meet-xin-making-cortana-understand-chinese/QOj0xoUMtpE