One of the greatest challenges of video game AI is that of creating believable companions that inhabit the world. Rather than being "alive" for merely seconds, they are engaged with the player for hours - and are often meant to be the focus. Complicating things further is when the companion is expected to be both leader and the follower, both dynamic and scripted, both the entertainer and the entertained. Architecting a system that handles all of these divergent needs can be daunting. This talk explains how these seemingly contradictory design goals of BioShock Infinite's companion character, Elizabeth, were solved by leveraging philosophies from other entertainment mediums, as well as one of Irrational's core design pillars. Using a detailed series of before-and-after videos, the talk will examine failures and successes in both design and implementation. It will also explain some of the techniques that can be used by other developers to improve their own companion AI characters.