[5] Robert's success on the race track along with his impish personality made him one of the most publicized and popular motocross racers of the early 1970s.

[2][6] He was known as one of the most naturally talented motocross riders of his era however, he was also notorious for his cigarette smoking and lack of physical training despite his portly physique.

Other times he would travel with fellow racers or, sometimes by train with his dismantled motorcycle packed into his hand luggage.

[10] After earning his expert class license in 1961, he switched to riding a Greeves and, won six races to finish second in the 250cc Belgian motocross national championship.

[9][10] He won 9 of the 14 Grand Prix races that year to clinch the world championship ahead of second place Torsten Hallman.

[21] After the 1967 World Championship season, Robert joined his ČZ factory teammates Roger De Coster and Dave Bickers, along with Husqvarna teammates, Hallman, Arne Kring and Åke Jonsson, in a series of exhibition races in the United States that had been organized by Edison Dye, the American importer for Husqvarna motorcycles.

[25] Olle Pettersson was hired from Husqvarna by the Suzuki factory to help develop their new motocross bike.

[25] After Robert won three consecutive Grand Prix races in France, Holland and West Germany to take the early points lead, Hallman then won three races in Russia, Yugoslavia and Sweden to tie Robert for the championship points lead as they went into the final round in Austria.

[26][2][27][28] He won six Grand Prix races during the 1969 season to successfully defend his world championship over second place Sylvain Geboers.

[32] For the 1970 season, Robert was wooed from CZ by the Japanese manufacturer Suzuki, who was seeking to make inroads into the European dominated sport.

[2] Robert continued to rule the 250cc world championship in 1971 by winning eight out of twelve Grand Prix races that year.

His record of 50 motocross Grand Prix victories stood for nearly 30 years until it was broken in 2004 by fellow Belgian, Stefan Everts.

[2] American Grand Prix motocross racer Jim Pomeroy commented on Robert's impressive physical strength in an interview, recalling how he watched him lift the rear end of a small car.

[41] Robert contracted COVID-19 in early 2021 during the COVID-19 pandemic in Belgium and was hospitalized but there he suffered a heart attack that left him in a coma.