Riel began performing on a Roman amateur stage where he became known as a villain actor. From 1909 to 1919 he was together with his wife, the actress Aidé Bongini, member of the acting troupe of Alfredo Sainati. In 1919 he got a contract with the film producer and director Enrico Guazzoni and in the following years became a frequently used actor of villains.
After his participation in Georg Jacoby's Quo Vadis? He came to Berlin in 1927 and for four years was often given major tasks in German film, especially as an adversary of Harry Piel . Then he went back to Italy and contented himself with a few supporting roles. From 1936 he worked mainly as a make-up artist and in 1937 took on a teaching position on make-up at the Centro Sperimentale di Cinematografia in Rome. He made a late appearance in the 1959 monumental film Ben Hur .
