Grasel was born into poor family of a knacker. Both his father and his mother helped themselves by stealing, occasionally ending in prison. Small Johann was forced to steal to survive and in age of 9 he entered prison for the first time (for two weeks). Grasel became leader several groups of brutal robbers in south Moravia and northern Lower Austria. He managed to escape from prison several times. In 1815 he and his group of 66 were caught by the authorities. Grasel was accused on 205 crimes, including several murders and sentenced to death. 60 thousands of people watched when he and his two colleagues were hanged.
Unlike many others of his kind Grasel entered folk legends, both as noble hero who takes from the rich to give the poor (not true) and as brutal rascal. The second variant made it into Czech language and the word grázl (it means villain) is now commonly used, even without knowledge of its origin.