Henri Becquerel (1852–1908) was a French engineer and physicist who was the first person to discover evidence of radioactivity. Born in Paris into a family that also included the engineers Antoine César Becquerel, Edmond Becquerel and Jean Becquerel, he studied engineering at the École polytechnique and the École nationale des ponts et chaussées, going on to take up positions at the National Museum of Natural History and the French government's Department of Roads and Bridges, before being appointed as a professor at the École polytechnique. For his work in the field of radioactivity he received the 1903 Nobel Prize in Physics, alongside Marie Curie and Pierre Curie. The SI derived unit for radioactivity, the becquerel (Bq), is named after him. This portrait of Becquerel is an albumen paper print from a glass negative taken by Paul Nadar.Photograph credit: Paul Nadar; restored by Adam Cuerden