Gustaaf Van Slembrouck was a Belgian professional cyclist from 1926 to 1934, nicknamed 'Den Staf'. He won 4 Tour de France stages, and wore the yellow jersey for 6 days in 1926. He finished in second place in the 1926 Paris–Roubaix. In the yellow jersey at the 1929 Tour de France after stage 5 — 1 stage, July 4 to July 4, taking it from Louis Delannoy. Wiki link