Evan James Williams FRS (8 June 1903 – 29 September 1945) was a Welsh experimental physicist who worked in a number of fields with some of the most notable physicists of his day, including Patrick Blackett, Lawrence Bragg, Ernest Rutherford and Niels Bohr. Williams earned a degree at Swansea University, doctorates at Manchester and Cambridge universities and a professorship at Aberystwyth University. He was highly regarded by his colleagues, and made a Fellow of the Royal Society in 1939. He died of cancer at the age of 42.