E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A bully; so called from Gradasso, King of Sericana, called by Ariosto the bravest of the Pagan knights. He went against Charlemagne with 100,000 vassals in his train, all discrowned kings, who never addressed him but on their knees. (Orlando Furioso and Orlando Innamorato.)