Lennox Cowie is a versatile astrophysicist who has made leading contributions across a wide range of theoretical and observational areas. His early work on energy transport processes in diffuse gaseous environments helped shape our understanding of the interstellar gas as a dynamic, multiphase medium. With Jeremiah Ostriker, he made a pioneering investigation of feedback processes during galaxy formation, and with James Binney he constructed one of the earliest theoretical models of cooling flows in rich clusters of galaxies. Observationally, Lennox pioneered the use of the newly available infrared arrays for deep survey work. He developed novel instrumental techniques enabling him to push ground based telescopes to new limits. With the Keck telescope, he has made significant contributions to our understanding of the high redshift intergalactic medium and was amongst the first to convincingly suggest that the peak of galaxy formation occurred quite recently.