* Robert Hooke: He was the first to observe and name cells in 1665.
* Anton van Leeuwenhoek: He was the first to observe living cells, including bacteria and protozoa, in the late 17th century.
* Matthias Schleiden: In 1838, he concluded that all plants are made up of cells.
* Theodor Schwann: In 1839, he concluded that all animals are made up of cells.
* Rudolf Virchow: In 1855, he proposed that all living cells arise from pre-existing cells.
Therefore, the answer to your question depends on who you consider a "major" contributor. Some might argue that Robert Brown, who discovered the nucleus in 1831, also played a significant role in the development of cell theory.
However, it's important to note that cell theory is a complex and evolving concept, and many scientists contributed to its development over time.
