Caspase-9 is an enzyme that plays a crucial role in the process of programmed cell death, known as apoptosis. It is part of a family of proteins called caspases, which are responsible for executing the death program in cells. Caspase-9 is activated in response to various cellular signals, particularly those related to stress or damage. Once activated, caspase-9 initiates a cascade of events that lead to the activation of other caspases, such as caspase-3, which ultimately results in the dismantling of the cell. This process is essential for maintaining healthy tissue and removing damaged or unwanted cells in organisms.