Blast From The Past G50:
Collect 20 Legendary Dwellers
This is probably one of the more annoying achievements in the game since the only ways to obtain Legendary Dwellers is either by doing a couple quests for 2 specific dwellers, or by opening lunchboxes and hoping you get lucky enough to receive a legendary dweller rather than a bunch of other junk. You can get more than one of the same dweller so when you have recruited 20 of them to your vault, your achievement will unlock.