The above episode TheGamerFromMars investigates “The Herobrine Theory” an urban legend in the Minecraft community.
Excerpt from Mincraftwiki page:
“Herobrine is the subject of a community-made “creepy-pasta” (Creepy story). He is one of the major community icons of Minecraft.
What Herobrine is
Herobrine is Notch’s dead brother, somehow embedded into Minecraft. While this is the “canon”, this is also completely false in reality, as Notch has no brother.
Herobrine is near-certainly inspired by Slenderman, who is also the inspiration behind Endermen.
The most popular theories among users is that Herobrine is a ghost. Other theories can involve him being a higher being, a demon, a bad omen, or the suggestions in the Canonical explaination. However, most of these are written as if Minecraft itself is reality, rather than from the player controlling the avatar within the game. Herobrine canonically has not appeared in real life, and remains confined to technology.”