You can now sign in two ways: with your Google account or with a DON Account, which is just an e-mail and a password. Create yours in the game itself or right here, at Create a DON Account.
With either one, your captain no longer lives on your phone: change devices, reinstall the game, sign in again and it is there, with everything you have earned. You can even keep both on the same captain.
Used to play as a guest? Link Google or a DON Account to your captain under Options › Account. It stays the same captain.
Forgot your password? Ask for a new one at Forgot my password. My account is also where you change your e-mail or password, or delete the account.