Ernest Rutherford (jan 1, 1913 – jan 1, 1914)
One of Ernest Rutherford's most prominent discoveries stated that atoms have a small charged nucleus that's surrounded by empty space, and that of which is surrounded by electrons. He also enhanced the understanding of the proton and the neutron in 1919. All discoveries of which aid in the understanding in the basic structure of the atom.
Added to timeline:
Atomic Theory project