The J. J. Thompson atomic model, also known as the "plum pudding model," was a proposed model of atomic structure where individual electrons were embedded in a cloud of positive charge. It was abandoned in favor of the modern model of a dense positively charged nucleus surrounded by a cloud of electrons. Sir Joseph John Thompson, the main proponent of this model, was also the first discoverer of electrons.
The J. J. Thompson atomic model was actually first proposed by Lord Kelvin, for whom the Kelvin absolute temperature scale is named, but Sir Thompson was its largest backer. He continued to be enthusiastic about it even after Lord Kelvin himself proposed alternate models. The model was disproved by the Rutherford gold foil experiment. In it, alpha radiation, which is actually composed of helium nuclei, was exposed to gold foil surrounded by a wall of zinc sulfide. The wall lit up whenever a helium nuclei hit it. It did not behave in a manner consistent with the J. J. Thompson model, and it had to be rejected in favor of the Rutherford model. The basic element of this model that is still accepted today is the existence of a small, dense nucleus. It was proposed by Ernest Rutherford after analysis of the experiment.