Oil painting, showing Callender half-length, seated in a wooden low-backed armchair, turned slightly to viewer's right against a mid-tone background, with his hands clasped in front and wearing black academic robes and hood. This recalls his early career on the naval teaching staff at Osborne and Dartmouth, and the Royal Naval College, Greenwich, rather than his final role as NMM's first Director.

Geoffrey Arthur Romaine Callendar was born at Didsbury, Manchester, on 25 November 1875, the elder son of a cotton mill owner: he also had sisters and - never marrying himself - was in later life their principal support. He was educated at St Edward's School and Merton College, Oxford, graduating in modern history in 1897. In January 1905 he joined the new Royal Naval College, Osborne, where he first embraced the study of naval history but, finding no suitable teaching textbook for cadets, rapidly wrote 'Sea Kings of Britain' (3 vols., 1907–11) and became head of the history and English department in January 1913. In 1921 he moved to the Royal Naval College, Dartmouth, as head of history, but as the subject's relevance in all levels of naval education was recognized after the First World War, rapidly progressed to become first Professor of History and English at the Royal Naval College, Greenwich, in 1922. His best-known work, 'The Naval Side of British History' appeared in 1924. From 1920 to his death he became both Secretary and Treasurer of the Society for Nautical Research as well, and was quickly involved in the SNR campaigns, first, to save HMS 'Victory' and subsequently to found what became the National Maritime Museum. In this he was the driving figure, not least since at Greenwich he had encountered both the existing Naval Gallery in the Painted Hall (since 1824) and the Royal Naval Museum, which arrived with the College in the former Greenwich Hospital buildings from 1873. He immediately recognized the value of both these near-moribund holdings as potentially part of a then non-existent national museum of Britain at sea - the absence of which had been highlighted by the great Naval Exhibition at Chelsea in 1891.

Formation of such a museum was already one of the Society's aims after securing the future of 'Victory' and, under Callender's guidance, it crystallized in a public campaign to save the huge Macpherson Collection of naval and nautical prints from sale abroad. This failed to reach its target, at which point (Sir) James Caird, a member of the Society, a key player in the 'Victory' project and Callender's main coadjutor thereafter, stepped in and himself bought the collection in 1928. It was placed in Callender's care at Greenwich, vested in the new Trustees of the National Naval and Nautical Museum Trust, of which both men were members. Shortly afterwards, Government agreed that the former buildings of the Royal Hospital School at Greenwich (those centring on the Queen's House) would become the new museum after the School left, which it did in 1933.

The National Maritime Museum Act was passed in 1934 and Callender became first Director. Apart from restoration of the House, the initial conversion and fitting of buildings (only completed in 1951) was largely funded by Caird, the entire Museum developing thereafter to Callender's plan. It was opened by George VI on 27 April 1937. Callender was knighted in 1938, steered the Museum through the Second World War and - with Caird in close continuing support - also began its post-war reconstruction. This was cut off by his death, suddenly but fittingly in his office of a heart attack on 6 November 1946, aged 70. As Director, and with a very small staff, Callender was an exacting autocrat but also a warm personality, with great diplomatic skill in getting what he wanted, a born conversationalist and teacher and (though not a great naval historian as a writer) a man of huge knowledge in his subjects and with a passion for communicating them.