Henry Gwyn Jeffreys Moseley, a preeminent British physicist, passed away on August 10th, 1915 aged 27. Moseley made a number of contributions to physics during his short lifetime. During WWI he identified the atomic number of a number of elements and developed a way of testing atomic structures that previously had not been possible. This method would revolutionise nuclear physics in the decades to follow. His notable research also included X-ray spectroscopy, which allowed him to accurately measure the energies of electrons in atoms. Moseley also served in the Royal Engineers during World War I, and was promoted to 2nd Lieutenant while stationed in the Gallipoli peninsula. Henry Moseley died suddenly in Gallipoli, leaving behind him a successful career as a physicist. Despite his relatively short life, his groundbreaking discoveries are still widely studied and applied in modern physics.