This vault was constructed in a small cave but it's not known when the construction of Vault 77 began. The purpose of Vault 77 in the vault experiments was to be populated by only one man and a crate full of puppets labeled "P13X U.S. GOVERNMENT ISSUE PUPPET RATION", as a study of the human condition in being alone with toys modeled on living beings for sole company. The vault door was designed to close automatically when the only Vault 77 dweller came into Vault 77, and only to reopen months later.
The Vault 77 dweller, later known as the Puppet Man, entered in the vault on the same day of the Great War on 23 October 2077 as expected. After one hour, he started getting nervous and shouted to open the vault door because they had forgotten all the other vault dwellers. On March 23, 2078, he began to get depressed and cry in front of the vault door, but still didn't use the puppets. On February 4, 2079, he eventually began to inspect the puppets' crate and used two of them, a dog puppet and a king puppet. On February 23, 2079, he continued to familiarize with his puppets and named the puppet king the "King". By March 30, 2079, he had completely personified his puppets, the dog puppet being named "Reverend Hound" and served as the sheriff and the part time reverend, and another grandmother puppet which he named "Grandma". He celebrated the birthday of the "King" with "Grandma" on this day.
But before going to bed, a Vault Boy puppet that he'd missed earlier began to talk to him (which is probably a side effect of his isolation and a descent into insanity), which the other puppets don't. On March 31, 2079, during the dawn, the "King" is found dead. When the Puppet Man confronts the most likely suspect, the Vault Boy puppet, it told him that they had, in fact, done it together and must flee before "Reverend Hound" comes for them. The Puppet Man accompanied by the Vault Boy puppet, opens the vault door (which was no longer locked) only to find a giant radscorpion holding up a car in each claw. In December 2079, he somehow manages to leave Vault 77 with the Vault Boy puppet, befriending a giant ant which he takes as a mount in the wasteland, and Vault 77 was thereafter abandoned.
 List of puppets
List of known puppets from the puppets' crate and the names given to them by the Puppet Man.
- A Vault 77 jumpsuit can be found in Paradise Falls in Fallout 3, alongside an audio recording of an obviously worried slaver, saying how it scares the others and it should be burnt, and that "he" may be back for it. The slavers obviously fear "him", hinting that it may belong to the vault dweller who killed the slavers who captured him. The jumpsuit appropriately boosts one's melee and unarmed skills (given that these were the Puppet Man's ways of murdering).
- Despite its somewhat strange presentation, experiment, and not showing up in any Fallout game, Vault 77 is considered canon.
Vault 77 appears only in the official Fallout webcomic One Man, and a Crate of Puppets.