A Domain Controller is a server that manages network security and user access within a Windows domain. It authenticates users and computers, ensuring that only authorized individuals can access resources like files and applications. This centralizes management and simplifies the administration of user accounts and permissions. In addition to authentication, a Domain Controller stores information about the domain, including user profiles and security policies. It uses a directory service, such as Active Directory, to organize and manage this data, making it easier for network administrators to maintain and secure the network environment.