Joseph Reiser was one of the managers who led the Omega and Tissot group SSIH (Société Suisse pour l'Industrie Horlogère) after the Brandt family generation that had founded it. According to Wikipedia he took over the leadership of the group from Paul-Emile Brandt in 1955; the Grail Watch Wiki, a secondary enthusiast source, records him taking the post of administrateur délégué (managing director) of Omega on 1 October 1958, after the death of Robert Favre, and holding it until 1 August 1968, when Charles Brandt replaced him. Other secondary sources describe him as already president of SSIH when he took over Omega's management, and credit him with setting up subsidiaries in the main markets and extending distribution and after-sales service worldwide.
His years in charge were among the most successful in the company's history. The group kept growing, absorbing or creating companies including Lanco, which joined SSIH in 1965 with 1,000 workers in Langendorf, and Lemania, the maker of Omega's best-known chronograph movements. Omega launched the Speedmaster chronograph in 1957. NASA chose it as its official chronograph in 1965, and on 21 July 1969 Buzz Aldrin wore one on the Moon. By the 1970s SSIH was Switzerland's largest producer of finished watches and third in the world, and Omega outsold Rolex.
Sources are thin and conflict: Wikipedia dates his leadership from 1955, the Grail Watch Wiki from 1958 to 1968 as Omega's managing director. A birth date of 1897 on an aggregator site has not been verified, and Casadi has not confirmed his nationality beyond his Swiss career.