The story of green Steve goes like this:
I was playing Minecraft on the 1.8 update when I found a desert temple, like most players I broke the blue block and jumped down the hole.
I hit the block that sets off the TNT but, surprisingly, it did not go off.
A Steve-like mob came down from the hole where the blue block was and it looked like Steve, only green. It hit me and I appeared in a room made of bedrock filled with creepers. I was really freaked out so I exited.
I then went back the next day.
I was not in the creeper cave but in a forest.
It was like I had made a new world. I saw words come up that said "[Green Steve] I am coming". I felt kinda weird but I didn't know why.
Then I found a house. It had been my house in the world before only in a forest, not a desert. I went in. There was nothing. Then the green mob came in.
Then words came up that said "[Green Steve] Hello brother".
Then I just blew up. I had no idea what had happened.
I deleted the world
After that. I sent an email to one of the developers who had helped make Minecraft and he said "One of the developers wanted Green Steve in Minecraft, but we said no and we had caught him adding it in" If this story is true it could explain Herobrine and many other things.