A Domain Controller (DC) is a server in a Windows network that manages security authentication requests, such as logging in, within a domain. It stores user account information, enforces security policies, and authenticates users and computers. By centralizing these functions, a DC ensures that only authorized users and devices can access network resources. It uses protocols like Kerberos and LDAP to perform authentication and directory services. In larger environments, multiple DCs provide redundancy and load balancing, enhancing both security and reliability. The DC is a critical component in Active Directory-based infrastructures, making it essential for network management and protection.