Read.
Herobine is a was a hoax at first and if you seen him the mods or texturepacks might have him in it.

Herobrine first appeared in a single image detailing an encounter. It was posted on the 4chan's board, and gained very little attention. It stated how Herobrine had appeared in someone's single-player game, littering the map with various pyramids and tunnels. It is the first media to name him as Herobrine.

It was only later that Herobrine grew in popularity, when the Brocraft streamer "Copeland" photoshopped Herobrine into several screenshots to show to his chat. He had recently taken a liking to the story, and wished to be a part of it. After getting largely good reactions, he decided to stage a hoax. He has explained exactly how that took place in an email.

Getting loads of tweets and emails about Herobrine again. I don't have a dead brother, and he never was in the game. Not real. Never was. „
~ Notch on Herobrine.

That's part of it but read the full story more where that came from.

Read the full story here:
http://www.minecraftwiki.net/wiki/Herobrine

Like I said,If you have mods or texturepacks,People might have him downloaded.

Maybe not texturepacks but mods will most likely have him in it.
Say what you want to say but he is not real,He will never be.Its just a creepypasta like slenderman.
Notch will NEVER add him to the game.

~Sam.