Cappy is one half of Nuka-World mascots, Bottle & Cappy. He can also be seen in various Nuka-World advertisements, and in The Grand Tour sub quests icons. He is also the character used for the Hidden Cappy contest, in the glasses required to find the hidden Cappy clues.
Cappy and Bottle are kidnapped by a raider gang in the quest series "Nabbed from Nuka-World". After freeing them, the pair will appear in the vault sporadically. They provide a temporary 20% happiness increase to every dweller, regardless of which room they are in. After they leave, dweller happiness is returned to their previous level. Tapping either one of the mascots when they stop and dance will yield caps, with Bottle occasionally yielding Nuka-Cola Quantum.