Robert Millikan discovered the value of an electron's charge which helped scientist better understand the atom.
Ernest Rutherford disproved Thomson's model after he conducted his famous gold foil experiment. He showed that in the center of an atom there is a positive charge called the nucleus. This was showed when the laser beam went through the foil and some particles got shot back.
Neils Bohr came up with an idea of how the hydrogen atom would look like based on the quantum theory proposed by Planck. The electrons in the model would circle around the nucleus in certain energy levels.
Erwin Schrodinger took Bohr's model a step further and came up with an equation to show how likely it was to find an electron in a certain place in the atom. He made a model that became known as the quantum model.