The Central Processing Unit (CPU) of a computer is the main processor of the system, responsible for executing instructions and performing calculations. It is often referred to as the 'BRAIN' of the computer, as it is responsible for controlling all of the operations of the machine. The CPU is composed of several components, including an arithmetic logic unit, control unit, and registers. It is connected to other components of the computer, such as memory, input/output devices, and storage devices, through a bus. The CPU is responsible for interpreting and executing instructions from the user, as well as managing the resources of the computer.