HeroBrine probably was added by accident, then notch decided to add him into the game as a planned idea. The whole thing proves that HeroBrine was for real until 1.2 and not just a texture or a mod. The HeroBrine mod coudnt have been added when HeroBrine was first put on the forums, the mod must have came after Herobrine was removed in 1.2. The idea that Herobrine was Notch's brother is not true, He is probably a dead miner, which explains why, when he appears in Multiplayer, he is usually holding a diamond pickaxe. In game HeroBrine is said to be stronger than an enderdragon and can kill with a single punch, which explains why HeroBrine is never seen carrying a weapon or wearing armour. A familiar sign of HerobBrine is an "E" made out of glowstone which is the sign that he is following you in your game. After HeroBrine was photographed for the first time, Many people put fake HeroBrine textures on doors, and uploaded them as proof.
Top three HeroBrine signs:
A glowstone "E".
Animals with white eyes.
A breif description of HeroBrine.
He has the default skin, But with glowing eyes. HeroBrine is said to haunt your game, just waiting for you to come close so he can take your items.
But have YOU seen HeroBrine? post in the comments, give me diamonds and subscribe, CYA!
(btw check out my herobrine video at this link http://www.youtube.com/watch?v=ABy_zuskY5c&feature=plcp