Science and technology are intimately related, and advances in science often become possible with the availability of new instrumentation. This has certainly been the case in mass spectrometry, which is used in so many scientific disciplines. Originally developed as an instrument for research in physics it was used in the discovery of isotopes, their recognition as the fundamental species comprising the elements, and the investigation of elemental isotopic composition. Isotope ratio mass spectrometry is a metrological technique of the highest order, and has been widely used in chemical, biochemical, cosmochemical, environmental, geological, physical, and nuclear research. Mass spectrometry presently plays a key role not only in scientific research, but also in industrial operations. This paper highlights the role that Alfred Otto Carl Nier played in bringing mass spectrometry into the mainstream of science. Nier's career spanned a remarkable period in science, and he made crucial contributions to atomic weights, geochronology, isotope geochemistry, nuclear physics, and space science. He is widely viewed as the 'father of modern mass spectrometry', because of his genius with instrumentation, his innovations, and the generosity with which he shared his ideas and designs. It is timely to remember his fundamental work in mass spectrometry, particularly the development of the sector field mass spectrometer, which is still the instrument of choice for many isotope scientists some 66 years after its first appearance in 1940.