Julien Arpels (1884–1964), also called Jules, was born in Marseille, a son of the stone dealer Salomon Arpels and a brother of Estelle Arpels, wife of Alfred Van Cleef. After his father's death he joined his brother Charles and Alfred Van Cleef in the new house at 22 place Vendôme; Van Cleef & Arpels dates his arrival to 1908, while Wikipedia places him among the partners from 1906.
Inside the firm he looked after the business and management side, while his brother Louis led sales. In the 1920s, when American visitors urged the house to open in New York, Julien was given the task. The first seasonal New York boutique opened in 1929 and, according to his Wikipedia biography, closed soon after the Wall Street crash. The house returned for the 1939 New York World's Fair and settled at 744 Fifth Avenue in 1940, where it remains.
His three sons, Claude, Jacques and Pierre, joined the business in the 1930s and became partners in 1937 with their cousin Renée Puissant. With the outbreak of the Second World War, the family, which was Jewish, left Europe; Julien sent Claude to Harvard so that he could better serve the American clientele. After the war the three brothers ran the house, Claude heading the American business and Jacques becoming chief executive.
In 1945 he received the Legion of Honour in Washington from the French ambassador Henri Bonnet. He died on 8 April 1964 at his apartment in the Hampshire House in New York, aged 79.
The house dates his arrival to 1908; Wikipedia gives 1906. His Wikipedia biography is based mainly on his 1964 New York Times obituary, which Casadi has not read in full.