Yep, you need to take the Mysterious Stranger perk for him to appear.
http://fallout.wikia.com/wiki/Mysterious_Stranger
Also, dialogue with the Lonesome Drifter in New Vegas suggests that the Mysterious Stranger is his father, and if you recruit the Lonesome Drifter for the Aces Theater, he rewards you with the Mysterious Magnum, which plays the Mysterious Stranger theme whenever you draw/holster it.
http://fallout.wikia.com/wiki/The_Lonesome_Drifter
http://fallout.wikia.com/wiki/Mysterious_Magnum
http://fallout.wikia.com/wiki/Mysterious_Stranger
Also, dialogue with the Lonesome Drifter in New Vegas suggests that the Mysterious Stranger is his father, and if you recruit the Lonesome Drifter for the Aces Theater, he rewards you with the Mysterious Magnum, which plays the Mysterious Stranger theme whenever you draw/holster it.
http://fallout.wikia.com/wiki/The_Lonesome_Drifter
http://fallout.wikia.com/wiki/Mysterious_Magnum