On April 30th, 2012, a user whose name is still unknown posted about a Herobrine-like entity on the Minecraft forums. The OP post went like this:

"I had created a new Minecraft world on versions 1.2.5 on the peaceful difficulty, intending to immerse myself in the serenity of a Minecraft world void of the fear of deadly creatures. Spawning into the world, I found myself on an entirely flat chunk of grass, surrounded by chunks of cliffs and hills. Thinking this would make an interesting moment on a seed showcase, I hit F3 to view the seed, only to discover it was one zero. I recorded this fact anyway on Notepad, along with my system time at the world creation, 12:00 PM, April 30th, 2012 (Minecraft uses the system time for its world generation algorithm if no seed is manually inputted). There were convenient steps on a cliff chunk facing me, which I climbed up to the plateau above. As soon as my head passed the edge of the plateau, I noticed a gray figure sprint at superhuman speeds away from me, just catching a glimpse of it. Thinking it was a figment of my imagination, I continued forth.

(Entity Zero)