Bottle appears as a co-mascot of Nuka-World, in the DLC of the same name.
After freeing him and Cappy from the raiders, the pair will appear in your vault from time to time (about once in 30 minutes of active gameplay) and appear immediately the first time. They provide a temporary 20% happiness increase to every dweller in the vault, regardless of which room Bottle and Cappy are in. After they leave, dweller happiness is returned to their previous level. This can greatly help those who have many dwellers with low happiness. Tapping on Bottle while he is waving or dancing will produce bottle caps or 1-5 bottles of Nuka-Cola Quantum.