Lille Olympique Sporting Club, commonly referred to as LOSC Lille or simply Lille, was founded on September 23rd, 1944 as a result of the merger between two local clubs: Olympique Lillois and SC Fives. The union was orchestrated by Henri Jooris, then president of Olympique Lillois and Roger Delaplace, a leading figure in the SC Fives organization (source).
The newly formed team struggled initially but quickly found success in the late 1940s under the guidance of manager Andre Cheuva. In their first season (1945-46), they secured promotion to France's top division known as Division 1 (now called Ligue 1) after winning Division 2 North with an impressive record (source).
Their early successes included back-to-back championships in the Coupe de France - one of France's most prestigious domestic cup competitions - in 1946 and 1947, followed by their first-ever league title during the 1948-49 season (source). Notable players from this era include forward Jean Baratte who played over a decade for LOSC scoring over hundred goals across all competitions.