The first person to split the atom was Sir Ernest Rutherford, along with his colleagues Hans Geiger and Ernest Marsden, in 1919. Rutherford conducted an experiment known as the Rutherford gold foil experiment, where they bombarded a thin sheet of gold foil with alpha particles. To their surprise, some of the alpha particles were deflected at large angles, indicating that the atom contains a small, dense, positively charged nucleus.
This experiment provided evidence for the existence of a nucleus within the atom and led to the development of the nuclear model of the atom. Although Rutherford's experiment did not involve intentionally splitting the nucleus of an atom, it was a significant milestone in understanding the structure of the atom and paved the way for future discoveries, including nuclear fission. Nuclear fission, which involves the splitting of atomic nuclei intentionally, was first achieved by Otto Hahn and Fritz Strassmann in 1938.