The initial user with administrative privileges for vCenter Single Sign-On is:

The initial user with administrative privileges for vCenter Single Sign-On is administrator@vsphere.local. This user account is automatically created during the installation of vCenter Server and is designed to facilitate the initial setup and configuration of the vCenter environment. The administrator@vsphere.local account has full access to all objects in the vSphere environment and can perform all administrative tasks, which is crucial for the initial setup.

This particular username aligns with the general convention for administrative accounts in many software platforms, providing clarity and consistency for those familiar with the environment. Users are encouraged to utilize this account for first-time logins to manage the vCenter Server settings, user roles, and permissions throughout the deployment.

Other account choices, while similar, are either not standard or do not represent the default administrative account provided by the system, thus serving different, typically less privileged functions.