The Universal Unique Identifier Also known as UUID, or as we refer to it Unique User ID, is the random text, assigned to you by the game, when you register. It cannot be changed, and is used to access all the information related to the user from the database.
Unlike your password, UUID is public, you can get your UUID by
visiting your profile and copying the text after
"#profile/" in the URL. This way you can access the UUID of any player in the game.