Answer:
The "Father of Modern Cell Theory" is Matthias Schleiden.
Matthias Schleiden was a German botanist who, in 1838, proposed that all plants are composed of cells. This was a significant contribution to the development of cell theory. Schleiden's observations and experiments led him to conclude that cells were the fundamental building blocks of plants and that all plant tissues are made up of cells.
Schleiden's work was further expanded upon by Theodor Schwann, a German physiologist, who extended the cell theory to include animal tissues as well. Together, Schleiden and Schwann formulated the cell theory, which states that all living organisms are composed of cells, cells are the basic units of structure and function in living organisms, and new cells arise from pre-existing cells.
It is worth noting that while Schleiden and Schwann are often credited as the founders of modern cell theory, their work built upon the observations and discoveries of earlier scientists, such as Robert Hooke and Anton van Leeuwenhoek, who first observed and described cells in the 17th century.