Democritus was the first scientist to create a model of the atom. He was the first one to discover that all matter is made up of atoms. His model was just a round solid ball. Democritus didn't know about a nucleus or electrons, all he knew was that everything is made of atoms.
John Dalton was an English chemist that created the Atomic Theory of Matter. He included in this theory that all matter is made of atoms, that atoms cannot be created nor destroyed and also, atoms of different elements combine in whole ratios to form chemical compounds.
J.J. Thomson discovered the electron, which led him to create the "plum pudding" atomic model. In this model, he thought that the atom was mostly positive, and negative electrons wandered around the atom.
Ernest Rutherford created the nucleus in the model, and said that instead of the positive matter being the whole atom, it was just in the middle. He said the atom was mostly empty space and that the electrons surrounded the positive nucleus.
Niels Bohr was a Danish scientist that was a student of Rutherford. He decided to make a new model based off of Rutherford's model, but changed the orbit of the electron. Also, he created energy levels in the atom. Bohr also used Planck's ideas in order to create quantum mechanics.
Louis de Broglie was a french physicist best known for his research on quantum theory and for predicting the wave nature of electrons.
Erwin Schrodinger was an Austrian scientist that worked with the Quantum model of the atom. He thought that the only way to find the location and energy of an electron in an atom was to calculate its probability of being a certain distance from the nucleus.
Werner Heisenberg was a German scientist that proposed the uncertainties of the Quantum model. He said that you can't know the exact velocity and momentum of the electron at the same time, which means you can't know the exact location of the electron.
Jame Chadwick was an English scientist that discovered the neutron. It made sense that the atom was neutral because the negative electrons and the positive protons cancelled out. Chadwick then found that the missing component was a neutral part: the neutron.