Sir Gilbert Thomas Walker (1868-1958) was a British mathematician and meteorologist, who became Director-General of Observatories in the Indian Meteorological Service. Aware of the extreme importance of the monsoon he began extensive statistical studies of correlations with worldwide meteorological data. In 1923 he published his findings on the Southern Oscillation.
His work was not of practical use at the time, but the significance of his results has subsequently been fully appreciated. The Walker Circulation, which he first described, is named after him.