Dr Brian Boyle has played a world-leading role in the study of cosmology. In the late 1980s/early 1990s, he changed the paradigm on our understanding of the cosmological evolution of quasars, initially in the optical and later in the X-ray domain. He also played a major role in uncovering the origin of the cosmological X-ray background, including leading the team which first identified star forming galaxies as a major constituent of the X-ray background. More recently he led the team responsible for creating the largest ever sample of quasars. This led to a number of breakthroughs, including a direct determination of the black hole mass function and the clustering of quasars at high redshift.