OK so I understand the creepypasta. Herobrine is actually a human from alpha. You know that monster mob that you see in the mob list with Single Player Commands on 1.0 - 1.2.5? That's a human, and a human is the real Herobrine. Now that one part where he sees a human could be true. But with the leaves cut without lava near, 2 block high tunnels, and that stuff wouldn't have happened. The 404'd Herobrine user on the Minecraft forums might've been a moderator that messaged him "stop" and immediately erased the user to troll the player. I got a new add-on with the stuff after the player see's Herobrine. It might be a map glitch or a creation that he doesn't remember making.
Now let's just move on with the topic...
I'd like to think of Herobrine as a network hacker that hacks into other peoples games dressed as the user Herobrine. If you go to
Miner Shoes and search for "Herobrine" without quotations, you can see the skin of a free account, but with his eyes white.
I can also think of him as a hacker, still, but angry at Notch. He gets revenge on him by hacking himself into games to scare the players and make them quit Minecraft just to make Notch upset.
Finally, I'd think of him as an op on a server that trolls the player, disguised as Herobrine.
That's all my thoughts. I'd rather you guys think into reality to find the truth of Herobrine.