Archimedes of Syracuse (c. 287 – c. 212 BC) was a Greek mathematician, physicist, engineer, inventor, and astronomer. He made significant contributions to various fields, and some of his key achievements include:

• Archimedes' Principle:
  This principle of buoyancy states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces. It is fundamental to understanding buoyancy and hydrostatics.
  Source: Britannica - Archimedes' principle
• Inventions and Engineering:
  Archimedes is credited with inventing numerous mechanical devices, including the Archimedes screw (a water pump still used in some parts of the world), compound pulleys, and defensive war machines like the claw of Archimedes.
  Source: Science and Industry Museum - Archimedes screw
• Mathematics:
  He developed methods for calculating areas and volumes of curved surfaces and solids. Archimedes also devised a method of exhaustion that anticipated integral calculus, and accurately approximated Pi (π).
  Source: School of Mathematics and Statistics - Archimedes