Isidore Montague Gluckstein (2 November 1890 – 16 January 1975) was managing director, then chairman, then president of J. Lyons and Co., a restaurant chain, food manufacturing, and hotel conglomerate created in 1884 that dominated British mass-catering in the first half of the twentieth century.^[1]

Isidore Montague Gluckstein was the son of Montague Gluckstein, chairman of J. Lyons and Co.^[1] He was educated at St Paul's, followed by Sidney Sussex College, Cambridge, and was severely wounded in World War I.^[1]

He was managing director of J. Lyons and Co. from 1940–56, chairman from 1956-61, and president from 1961.^[1]