How did scientists discover that all living things are made of cell?

The first cell was discovered and named by Robert Hooke in 1665. he remarked that it looked strangely similar to cellular or small rooms which monks inhabited, thus deriving the name. However what Hooke saw actually saw was the dead cell walls of plant cells

All living things or organisms are made of cells ... By learning about cells and how they function, you can learn about all types of living things. Credit for developing cell theory is usually given to three scientists: Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow.