Lambert Simnel (1477?-c. 1525): Juvenile pretender to the English throne. In 1485, Richard III was overthrown by Henry VII -- who, however, had a real problem in that it took an incredibly twisted line of argument to make him the proper king (he was descended from the third son of Edward III, but there were many descendants of the second son, plus Henry VII's descent involved illegitimacy). The result of this was that a large fraction of the population wanted him off the throne. Plus Richard III had set aside the rightful King Edward V, and neither Richard nor Henry ever showed what happened to him. The result was a number of "feigned boys" -- youths offered up as claimants to the throne senior to Henry Tudor. Lambert Simnel was the first of these. A priest named Richard Symonds made the claim that Simnel was Edward, Earl of Warwick, son of George, Duke of Clarence and the first cousin of the deposed Edward V.
One minor problem: Warwick was still alive. Henry VII showed him off -- then defeated Simnel and his followers at the Battle of Stoke in 1487. Simnel, because he was so young (only about ten) was pardoned and made a royal servant; he survived for about fifty more years.
It was the last time Henry VII would be so merciful.