Vault 77

A lot of people know about this Vault, despite the fact that it has, and most likely never will appear in any Fallout game. The guys from Penny Arcade were so jazzed up for Fallout 3 that they created their own comic for the game, depicting a story of one man locked in a Vault alone with a box of puppets. The man (Real name unknown, although he's reffered to as "The Puppet Man".) In this story, The Puppet Man first enters Vault 77 and tries deperatly to get out after realizing that he's all alone. After more than a year, he finds a box of puppets and begins playing with them, finally giving them all personalities and even beliving that they're real ("The King", "Reverand Hound", and a grandma Puppet.) One day, the Puppet Man discovers a Vault Boy puppet in the same crate as he found the other puppets. He discovers that the Vault Boy Puppet killed the King, and the puppet claims that the Puppet Man was his accomplice. Fearing Reverand Hound, The Puppet Man leaves Vault 77 (Despite not being able to when he first got in...) only to immediatly jump back in after seeing a giant Radscorpion. He leaves the net morning and has several adventures through the wastes (Including domesticating a giant ant named "Mr. Pinch" and meeting a Ghoul resident of one of the other vaults, possibly Vault 13.) before finally being caputred by Slavers. The Puppet Man pleeds them to run away, claiming that the Vault Boy puppet was a killer. While trying to decide if he should be kept for a slave or made into food, it is assumed that the Puppet Man escapes, beats one of the slavers to death, and nearly kills the other, who runs back to their base. While trying to tell the others about what happens, The Puppet Man finds the base. It is assumed that he then killed everyone within. The comic ends with The Puppet Man standing, enraged, in the middle of the wastes covered in blood, with a cryptic message: "But you have to remember, the Vaults were never meant to save anyone."

Apparently Bethesda liked this comic, because there's an Easter Egg for it hidden in Fallout 3. In the back of the barracks of Paradise Falls, you'll find on a shelf a Vault 77 Jumpsuit next to a holotape labled "Burn this Goddamn Jumpsuit!" explaining that it's freaking out the other slavers because of a ghost story. He also mentioned that they feared that the original owner might come back for it. It gives +5 to Melee Weapons and Unarmed, the Puppet Man's preferred methods of killing. Some players claim that getting this Jumpsuit will cause The Puppet Man to randomly attack you, but this is most likely untrue, as there is no evidence of it.

I personally find this Easter Egg quite amusing and cool, it shows that Bethesda keep their minds and ears open to the fans.

How would he attack you anyways? If they have his Vault Jumpsuit then he's most likely dead or something so doubt he could kill you.

He's not in the game, it was just a rumor sparked after the holotape was heard, someone thought that The Puppet Man might attack you to get his Jumpsuit back, but this is probably nonsense.

Could you provide a link to the story please?

The comic by Penny Arcade, or like it's Fallout wiki page?