Martin John Rees, Baron Rees of Ludlow, OM, PRS (born 23 June 1942 in York) is an English cosmologist and astrophysicist. He has been Astronomer Royal since 1995, and Master of Trinity College, Cambridge since 2004.
After holding post-doctoral research positions in England and the United States, he taught at Sussex University and the University of Cambridge, where he was the Plumian Professor until 1991, and the director of the Institute of Astronomy. From 1992 to 2003, he was Royal Society Research Professor, and from 2003 Professor of Cosmology and Astrophysics. He was Professor of Astronomy at Gresham College, London, in 1975 and became a Fellow of the Royal Society in 1979. He also holds Visiting Professorships at Imperial College London and at the University of Leicester. In 2008 he received an honorary doctorate from Yale University. He also received an honorary doctorate from McMaster University, in Hamilton Ontario, on June 9, 2009. He is also a Member of Council of the Royal Institution of Great Britain. Rees is the author of more than 500 research papers, and he has made important contributions to the origin of cosmic microwave background radiation, as well as to galaxy clustering and formation. His studies of the distribution of quasars proved to be a nail in the coffin of the Steady State theory. He was also one of the first to propose that enormous black holes power quasars. He is also a well-respected author of books on astronomy and science intended for the lay public.
On 22 July 2005, Rees was elevated to a life peerage, sitting as a crossbencher in the House of Lords. On 6 September, he was created Baron Rees of Ludlow, of Ludlow in the County of Shropshire. In 2005, he was awarded the Crafoord Prize. He became President of the Royal Society on 1 December 2005.  He is an advocate of the memory of Joseph Rotblat. He has taken to speaking about humanity's future on Earth.
* Heineman Prize (1984)
* Gold Medal of the Royal Astronomical Society (1987)
* Balzan Prize (1989) for High Energy Astrophysics
* Knight Bachelor (1992)
* Bruce Medal (1993)
* Bruno Rossi Prize (2000)
* Gruber Prize in Cosmology (2001)
* Henry Norris Russell Lectureship of the American Astronomical Society (2004)
* Lifeboat Foundation's Guardian Award (2004)
* Royal Society's Michael Faraday Prize for science communication (2004)
* Life Peerage (2005)
* Crafoord Prize, with James Gunn and James Peebles (2005)
* Order of Merit-the personal gift of The Queen (2007)
* Caird Medal of the National Maritime Museum (2007)
Named after him
* Asteroid 4587 Rees
Sir Martin Rees: Earth in its final century? watch!http://www.ted.com/index.php/talks/view/id/42
ted.com — In a taut soliloquy that takes us from the origins of the universe to the last days of a dying sun 6 billion years later, renowned cosmologist Sir Martin Rees explains why the 21st century is a pivotal moment in the history of humanity: the first time in history when we can materially change ourselves and our planet.