In an interview with Famitsu, Hideo Kojima gave some more details on the AI buddy system in Metal Gear Solid V: The Phantom Pain. Translations by JunkerHQ.
According to Kojima, you will be able to choose from a variety of buddies. We already know Quiet and DD the wolfdog are among them. However, Kojima mentions you have to choose carefully when taking along soldiers you’ve extracted, since they were originally your enemies. When talking about Quiet during the Tokyo Game Show, he mentioned a ‘bond system’ that determines the actions she can perform, so maybe that’s something that goes for all allies.
Also, if you have your buddy kill a lot of enemies, it will bring down your score.
And no, Kojima will not appear as a buddy in the game. “If I got you spotted you might take it out on me.” Hopefully he will at least be at Mother Base if you’ve rescued him in Ground Zeroes.
Source: Famitsu, JunkerHQ Twitter