Martin John Rees, Baron Rees of Ludlow, (born 23 June 1942) is a British cosmologist and astrophysicist. He is the fifteenth Astronomer Royal, appointed in 1995, and was Master of Trinity College, Cambridge, from 2004 to 2012 and President of the Royal Society between 2005 and 2010. He has received various physics awards including the Wolf Prize in Physics in 2024 for fundamental contributions to high-energy astrophysics, galaxies and structure formation, and cosmology.