Mysterious Stranger (Fallout)

Mysterious Stranger is a perk in Fallout and Fallout 2.

Effects
Only in hostile random encounters, there is a chance that the character will gain a temporary ally in a leather jacket (male with a male character and female with a female character). The unidentified stranger's details depend on the player character's level.
 * $$\text{Chance of appearance }\%=30+(2\times\text{Luck})$$

Fallout
The Mysterious Stranger remains on the map of the random encounter even after the end of the fight, until leaving. The stranger can be spoken to, but will not say much.

Fallout 2
Unlike in Fallout, the Mysterious Stranger will now leave the map of the random encounter directly after ending combat. A few exceptions to this are caravan encounters and encounters with a cave included.

Behind the scenes

 * The Mysterious Stranger perk was originally designed by Scott Bennie.
 * There were several unfinished drafts of a book by Mark Twain titled "The Mysterious Stranger," in which the title character claims to be Satan's nephew, and which contain various references to the number 44.

Bugs

 * The Mysterious Stranger with a hunting rifle actually spawns shotgun shells as ammunition instead of .223 FMJ.
 * In Fallout 2, if the game is saved during a random encounter with the Mysterious Stranger still being on the map, and then reloaded, the Mysterious Stranger will remain in place.