Final answer:
Rudolf Virchow is credited with popularizing the idea that 'all cells come from pre-existing cells' in 1855, though Robert Remak had first published the concept in 1852. This principle is a fundamental part of the cell theory, which was also influenced by Matthias Schleiden and Theodor Schwann's earlier work.
Step-by-step explanation:
The person who concluded that "all cells come from pre-existing cells" was Rudolf Virchow. He popularized this concept in 1855 through his essay entitled "Cellular Pathology". However, Robert Remak first published this idea in 1852, which eventually led to a controversy regarding the proper attribution of this contribution to the modern cell theory.
In the 1830s, Matthias Schleiden and Theodor Schwann laid the foundation for this theory by proposing that all living things are composed of one or more cells and that the cell is the basic unit of life. They also suggested that new cells arise from existing cells. This fundamental understanding of cell biology has been pivotal in advancing our knowledge of living organisms and their functions.
Despite his recognition, Virchow's failure to credit Remak's earlier work on cell division and the generation of new cells from existing ones remains a point of ethical contention in the scientific community. The work of these scientists collectively contributed to the unified cell theory, which is a crucial element in biology and the study of life.