Alexander Dalgarno passed away peacefully on April 9, 2015. Born in 1928 and raised in London, he studied mathematics and theoretical atomic physics at University College London. He was a talented soccer (football) player and enjoyed playing tennis and squash into his ninth decade. He became a professor at the Queen's University of Belfast and later joined Harvard University's Astronomy Department in 1967, served as its chairman, and became the Phillips Professor of Astronomy. His contributions led to the recognition that none have been greater "in the history of atomic physics and its applications" and he has been called the "father of molecular astrophysics." He established the influential Institute for Theoretical Atomic and Molecular Physics at the Harvard-Smithsonian Center for Astrophysics. He was a recipient of many awards, including the Benjamin Franklin Medal in Physics, the Royal Society's Hughes Medal, the Royal Astronomical Society's Gold Medal, the American Geophysical Society's Fleming Medal, and the Royal Society of Chemistry's Spiers Medal.. He was even honored by having an asteroid named after him. He was a gifted mentor to generations of students, a generous and inspiring colleague, and a humanist in every respect. He is survived by his four children, Penelope, Rebecca, Piers and Fergus, seven grandchildren, and by his partner Fern Creelan. Memorial service details will be forthcoming. In lieu of flowers, please make a contribution in his honor to the Equal Justice Initiative, 122 Commerce St., Montgomery, AL 36104, at https://donatenow.networkforgood.org/eji.