He's the mysterious stranger. When you hear the music, you have to find him and click on him. If you click on him, he disappears and you get a random amount of caps. If you don't click on him, he disappears and randomly murders one of your dwellers.
Shhhh! It's fun messing with people who don't read patch notes.
I was so excited when 1.2 rolled out and introduced the Mysterious Stranger.
Then I found him and clicked on him. Just what I need, more CAPS.
id would of liked it better if the mysterious stranger showed up to help take care of deathclaws or mole rats.