The cell theory, which is comprised of three different but related elements, was discovered and developed by Matthias Schleiden, Theodor Schwann and Rudolph Virchow. All three men were scientists in Germany who lived during the 1800s, but they did not work together to develop the theory.
The first part of the cell theory states that all living things on Earth are comprised of cells; this portion of the cell theory was determined by botanist Matthias Schleidan. The second part, determined by zoologist Theodor Schwann, states that cells make up the basic units of every living thing. Physician Rudolph Virchow was responsible for the third part, which states that living cells stem from other living cells.