Although the early Greek philosopher Democritus hypothesized the existence of atoms, it was not until the late 1800s that English physician J.J. Thomson proposed a model for the atom. J.J. Thomson discovered the atom because of his discovery of the electron, which was a very significant discovery in the field of physics.
Although J.J. Thomson is generally credited with creating the first proposed model of the atom, there were many scientists who also advanced the concept of the atom and the electron. Some of these scientists include Max Planck, John Dalton, Albert Einstein, Ernest Rutherford and Niels Bohr. Theories of the atom continue to advance in the 21st century.