Characters within the game range from enemies to your own citizens. Vault citizens are known as dwellers and players have taken to calling enemies invaders.
Rare dwellers are found in lunchboxes. Their names are randomly generated. Each arrives wearing a rare outfit or carrying a rare weapon. Rare dwellers keep their outfit when entering the vault, rather than immediately switching to a vault suit.
There are 23 different legendary dwellers to collect. These are named after main characters from Fallout 3 and Fallout 4. Legendary dwellers are found randomly through opening lunchboxes. Legendary dwellers have a total sum of 40 SPECIAL points.
Legendary dwellers are not unique. A vault can have multiple legendary dwellers of the same name. All legendary dweller cards are equally likely to be found in a lunchbox, regardless of whether any legendary dwellers are already in the vault.
Some Legendary dwellers, such as Sarah Lyons and Preston Garvey, can be obtained by completing their respective quests from the Overseer's office.
Abraham Washington initially has an outfit that has no name and provides no bonuses. Despite the fact that the in-game Washington is wearing a blue shirt with a green pullover, the outfit's icon is the same white, long-sleeve, button-down shirt icon that a new dweller has before he is brought into the vault. This icon only appears in Abraham Washington's infobox; the outfit selection pane shows no icon, name, or bonus. If this outfit is replaced, it does not enter your inventory, and thus cannot be given to any dweller; Washington cannot return to this outfit once changed.  UPDATE: This changed with the 1.5 release. Abraham Washington now comes equipped with Abraham's relaxedwear. If you previously changed his outfit, the relaxedwear appears in your inventory.
Characters' SPECIAL stats differentiate from their counterparts in other Fallout games. Characters may also be using referenced weapons that they normally wouldn't be using in their other respective appearances.
The original twenty legendary dwellers available in Fallout Shelter version 1.0 are based on characters from Fallout 3. Dwellers added through updates are either based on the Fallout series in general or Fallout 4. Mr. Handy and Preston Garvey were added in version 1.1, and the Mysterious Stranger and Piper were added in version 1.2. Old Longfellow was added in version 1.5, for a limited time you could obtain him in a special event started May 12th, plus 5 lunchboxes, but only in a single vault that you opened first when this event was launched.
The Mysterious Stranger only appears in the vault for a few seconds, and will disappear after this time has passed or the player selects him to collect caps. He is not able to be a dweller, as all other characters are.