Herobrine for Bukkit or Spigot (or just "Herobrine" for short) is a derivative of the Herobrine AI plugin for Bukkit, originally written by Bukkit plugin developer Jakub1221. This derivative is intended to maintain a rapid release cycle in an effort to patch bugs more frequently and also to try to update to the newest release of Bukkit/Spigot faster so that server administrators will be able to continue to have Herobrine stalk the players on their Minecraft server.
https://www.theprogrammersworld.net/Herobrine/