On the Genealogy of Morality contains some of Nietzsche's most disturbing ideas and images: eg the 'slave revolt' in morality, which he claims began with the Jews and has now triumphed, and the 'blond beast' that must erupt, which he claims to find behind all civilisation. It is therefore a major source for understanding why 'Nietzschean' ideas are controversial. Further, it is one of Nietzsche's most important books, a work of his maturity that shows him at the height of his powers both as a thinker and as an artist in the presentation of ideas.