Herobrine is an unknown entity. He is tall, strong, and holds a lot of power. He's rather serious and has no tolerance to most players. He's ominous, cold, calculating, omniscient, and mysterious, but he isn't evil.
He avoids interacting with players, but at times, he may find himself reluctantly helping a player he has taken an interest in. He might even share some knowledge and stick around. Other times, he reveals himself to a player he deems a nuisance to the world to teach a lesson.