Ctesibius was an ancient Greek engineer and inventor, known for his work in the field of hydraulics. He lived in Alexandria around the 3rd century BCE and is often credited with creating the first known water clock, or clepsydra, which measured time using the flow of water. His innovations laid the groundwork for future developments in engineering and mechanics. In addition to the water clock, Ctesibius invented various devices, including the pneumatics that utilized air pressure. His contributions significantly influenced later scientists and inventors, such as Hero of Alexandria, who built upon his ideas in their own work.