Edmond Jaeger was a Paris watchmaker and official supplier of instruments to the French Navy. In 1903 he challenged Swiss manufacturers to produce the ultra-thin movements he had designed. Jacques-David LeCoultre, grandson of Antoine LeCoultre and head of production at LeCoultre & Cie in Le Sentier, took up the challenge, and in 1907 the firm produced the LeCoultre Calibre 145, at 1.38 mm the thinnest watch movement in the world.
That year Cartier, one of Jaeger's clients, signed a contract with him reserving all Jaeger movements for its exclusive use for fifteen years; the movements were made by LeCoultre. In 1917 Jaeger and LeCoultre formed a partnership to run their businesses together while remaining separate companies, and between the wars Jaeger's Paris house absorbed about three-quarters of the Swiss manufacture's output. Jaeger also bought the patent for the Atmos clock, powered by changes in temperature, from its inventor Jean-Léon Reutter and licensed it to LeCoultre from 1936 for France and from 1937 for Switzerland. The collaboration led to the creation of the Jaeger-LeCoultre name in 1937. Casadi has not verified Edmond Jaeger's dates of birth and death.