Radioactivity was discovered by the French physicist Henri Becquerel in 1896. He found that uranium salts emitted rays that could expose photographic plates, a phenomenon later termed radioactivity. Marie Curie and her husband Pierre Curie conducted extensive research on radioactivity and discovered additional radioactive elements, including polonium and radium. Their work laid the foundational understanding of radioactivity, leading to significant advancements in both nuclear physics and medical applications, such as cancer treatment. Becquerel's critical discovery earned him the Nobel Prize in Physics in 1903, along with the Curies, marking a pivotal moment in scientific history.