Who were Robert Hooke Anton Van Leeuwenhoek Schleiden and Schwann and what were their contributions to the cell theory?

Robert Hooke was an English scientist who first described cells in 1665. Anton van Leeuwenhoek was a Dutch scientist who improved the microscope and observed single-celled organisms. Matthias Schleiden and Theodor Schwann were German scientists who contributed to the cell theory by proposing that all living things are composed of cells. Schwann also stated that the cell is the basic unit of structure and function in living organisms.