Answer:
Cell theory was given by Louis Pasteur and Rudolf Virchow which states that cells originate from the pre-existing cells and Omnis cellula e cellula, which means each cell comes from another cell respectively.
Before the cell theory, people believe that life originate from spontaneous generation, which state that living organism originates from non-living matter.
According to this theory, it was believed that dust creates fleas, maggot arises from the rotten meat, wheat and bread left in the dark corner produces mice.
Louis Pasteur was the first scientist to prove that cells originate from the pre-existing cells, which takes hundred of years to prove that.