Ernest Rutherford
Rutherford was one of the first researchers in nuclear physics, after the discovery of radiation by the French physicist Henri Becquerel in 1896. Rutherford discovered the radioactive half-life, and the three parts of radiation which he named Alpha, Beta, and Gamma. He also discovered that alpha particles were the nuclei of Helium. Rutherford's Geiger–Marsden experiment led to what we know today about the atomic structure, where the atom is a nucleus and electrons orbit around it.