A device driver in an operating system serves as a communication bridge between the OS and hardware devices. It facilitates the control and management of peripherals such as printers, graphics cards, and storage devices. By translating high-level commands from the operating system to hardware-specific instructions, device drivers enable proper interaction and functionality between the two. Without the appropriate driver, hardware may not function correctly or at all. This ensures that users have a seamless experience when connecting and using various devices in their computing environment.