This right here.
Puff didn't create B.I.G's personality. He A&R'd his music direction and worked on his palette to make the singles more radio-friendly. B.I.G. wasn't going around acting like someone he wasn't. Nobody that ever knew dude has said anything remotely close to that. What Puff adjusted, was some of the music to get radio spins and video play. He never told B.I.G. to act more this and that.
Pac was an actor and a theatre kid. So it's like Treach said, he would adapt his personality based on the people he was around in those moments. So when he was around street n*ggas, he would take on their aura. B.I.G. was always just acting like who he really was. Puff changed some of the music, not the dude's personality. WTF?