Glad you asked, many scientists came up with it together. Lets learn about them.
One of the Scientists was Robert Hooke. His contribution the cell theory was coming up with the word cell.
We shall call this a cell!
Robert Brown contributed to the cell theory by discovering the nucleus. The red object in the picture is an example of what the nucleus looks like.
I discovered the nucleus. The nucleus is what controls the cell.
Matthias Schleiden added to the cell theory by defining the basic unit of a plant structure. The picture below is what a plant cell looks like.
I have came to a conclusion that all plant cells have the same structure.
The next scientist is Theodor Schwann. He contributed to the cell theory by finding that all animal tissue is composed of cells.
I have came to a conclusion that all tissue is made up of cells, an example would be animal tissue. All animal tissue is made up of cells.
The last scientist we are going to talk about is Rudolph Virchow. His contribution to the cell theory was finding out that all cells are made of pre-existing cells. There are more scientists that helped add to the cell theory, but this is all we have time for.
According to my studies, I have found out that all cells are made from pre-existing cells.