All functioning Android phones, which are a looot, have at least one associated Google account, necessary for proper functioning.
The great growth in the market of these phones has made many people have a Google account or Gmail associated with their mobile, in some cases, only used for this purpose.
It often happens that the username and password required during the registration process are first entered into the phone and subsequently forgotten. At some point the system will ask us for this information again and if we do not remember it, we will have a problem.