The gold foil experiment, conducted by Ernest Rutherford, proved the existence of a tiny, dense atomic core, which he called the nucleus. Rutherford's findings negated the plum pudding atomic theory that was postulated by J.J. Thomson and made prior to the discovery of the nucleus.
Rutherford, known as the father of nuclear physics, is credited to have pioneered the theoretical concepts of the real nature of the atomic structure. During his gold foil experiment, Rutherford observed that a significant number of the alpha particles he used passed through the thin gold foil without a deviation in direction. He further noted that only a handful of particles got deflected and bounced off. Rutherford then concluded that the atom's mass was tightly-packed into a condensed kernel, now known as the nucleus.