A USB controller is a hardware component that manages the communication between a computer and various USB devices, such as keyboards, mice, printers, and external storage drives. It allows these devices to connect and transfer data efficiently, enabling users to expand their computer's functionality. The USB controller interprets signals from the computer's motherboard and translates them into a format that the connected devices can understand. It also handles power distribution to ensure that each device receives the necessary energy to operate. This makes it an essential part of modern computing, facilitating seamless interactions with a wide range of peripherals.