"Perkin Warbeck" was a pretender to the Kingdom of England/English throne.
By claiming to be Richard of Shrewsbury, Duke of York, the younger son of King Edward IV of England/Edward IV, one of the "Princes in the Tower", Warbeck was a significant threat to the newly established Tudor dynasty, and gained support outside England.
Henry VII declared Warbeck an impostor, and after his capture, Warbeck wrote a confession in which he said he was a Flemish people/Fleming born in Tournai around 1474.
Due to uncertainty as to whether Richard of Shrewsbury had died in the Tower of London or had survived, Warbeck's claim gathered some followers, whether due to real belief in his identity or because of desire to overthrow Henry and reclaim the throne. Dealing with Warbeck cost Henry VII over £13,000, putting a strain on Henry's weak state finances.More Perkin Warbeck on Wikipedia.
High and mighty king, your grace, and these your nobles here present, may be pleased benignly to bow your ears, to hear the tragedy of a young man, that by right ought to hold in his hand the ball of a kingdom; but by fortune is made himself a ball, tossed from misery to misery, and from place to place.Perkin Warbeck