His appearance takes place in The General, Part One of Foundation and Empire.
Cleon II, commonly called 'The Great'. Was the last strong Emperor of the First Empire, he is important for the political and artistic renaissance that took place during his long reign. He is best known to romance, however, for his connection to Bel Riose, and to the common man, he was simply 'Riose's Emperor'. During his later years he suffered from a painful and undiagnosed ailment. About 200FE, Cleon directed interest in the Origin Question was "stale and unproductive speculation that tends to undermine the people's love of the Imperial throne."
He declares war against the First Foundation in Terminus, of which his Privy Secretary Ammel Brodrig informs him after learning about Riose's actions. Brodrig informs his Emperor that Riose was in the Lemul Cluster, that he is one of the "popular generals", and that his soldiers are entirely under his command.