
The Mysterious Stranger appears in Fallout, Fallout 2, Fallout 3 and all its add-ons, Fallout: New Vegas and all its add-ons, Fallout 4 and all its add-ons, and Fallout 76.

He will spawn in intervals of at least 10 minutes. He can spawn at anytime, appears with a smoke poof and leaves with one as well. Finding him two, four, and five times, respectively, are three of the objectives. If any rooms are not powered he will not appear, even when the sound effect occurs. He must be tapped on to receive the caps. When selected, he disappears and the vault is awarded a random amount of caps based on how quickly he is found.

He does not aid in battles, but may appear in the vault regardless of if the vault is experiencing an incident. In Fallout Shelter, the Mysterious Stranger appears in vault rooms or elevators and a sound is played when he does so. If the Stranger kills an enemy while he is traveling as a companion, Nick will express incredulity when he appears, and frustration when he vanishes.

When the Courier draws it, the same guitar notes that are heard when the Mysterious Stranger shows up are played, and a chord is played when the weapon is holstered. 44 Magnum that looks similar to the Mysterious Stranger's. The Lonesome Drifter remarks about his past when speaking to the Courier, mentioning his father was a "mysterious" man, and a "stranger" to his own family.

During the add-on Mothership Zeta, having the Mysterious Stranger perk opens up a unique dialogue option with Somah, where the Lone Wanderer mentions if they are lucky, a friend might show up and help them.He can appear in water, and swim around.He circles around the enemy shooting several times.A short guitar riff will play whenever he holsters or upholsters his weapon, as does the Mysterious Magnum.
