Which French physicist discovered radioactivity in 1896?

Henri Becquerel discovered radioactivity in 1896. While investigating whether uranium salts emitted X-ray-like radiation after exposure to sunlight, he found that the salts affected photographic plates even when kept in darkness.

Becquerel had placed uranium compounds on plates wrapped in opaque material. Several days of cloudy weather prevented the sunlight-driven experiment he had planned, so he stored the plates in a drawer. When he developed them, the images were unexpectedly strong. Further tests showed that uranium produced penetrating radiation spontaneously, without needing prior exposure to light.

The discovery launched intensive research into atomic radiation. Marie and Pierre Curie studied the phenomenon, coined the term radioactivity, and discovered the elements polonium and radium. Becquerel, Marie Curie, and Pierre Curie shared the 1903 Nobel Prize in Physics for their work.

Ernest Rutherford later investigated the nature of radioactive emissions, while Marie and Pierre Curie expanded the list of radioactive elements. They were major contributors, but the original 1896 discovery of spontaneous radioactivity is credited to Becquerel.