Sir Thomas Ranken Lyle FRS (26 August 1860 – 31 March 1944) was an Irish-Australian mathematical physicist, radiologist, educator, and rugby player. Lyle was born and educated in Ireland before emigrating to Australia to take up a professorship at the University of Melbourne. There he was a pioneer in the use of X-rays as a medical tool. The Thomas Ranken Lyle Medal is awarded in his name to honour Australian achievements in Physics and Mathematics.