built-in Administrator

On Windows-based computers, a user account that is a member of the computer’s local Administrators group or a member of a group that is a member of the local Administrators group, such as the Domain Admins group in a Windows domain. This is the first account that is created when you install an operating system on a new workstation, stand-alone server, or member server. By default, this account has the highest level of administrative access to the local computer.