Riccardo Giacconi (/dʒəˈkoʊni/ jə-KOH-nee, Italian: [rikˈkardo dʒakˈkoːni]; October 6, 1931 – December 9, 2018) was an Italian-American Nobel Prize-winning astrophysicist who laid down the foundations of X-ray astronomy.

Born in Genoa, Italy, Giacconi received his Laurea from the Physics Department of University of Milan before moving to the US to pursue a career in astrophysics research.

In 1956, his Fulbright Fellowship led him to go to the United States to collaborate with physics professor R. W. Thompson at Indiana University.

This was followed by Director General of the European Southern Observatory (ESO) from 1993 to 1999, overseeing the construction of the Very Large Telescope, then President of Associated Universities, Inc. (1999-2004) managing the early years of the ALMA array.

Giacconi was awarded a share of the Nobel Prize in Physics in 2002 "for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources".