The following has been taken from the since deleted Wikipedia page http://en.wikipedia.org/wiki/William_Gardner_(knight) - on  his identity is doubted. The page is kept for reference/interest.
Sir William Gardiner (c. 1450 - c. 1485) London, Clothe Merchant Brother of Sir Richard Gardiner Sheriff, Alderman Walbrook Ward, Lord Mayor of London.. William Gardiner is noted for killing King Richard III of England on 22 August 1485 at the Battle of Bosworth Market. Both William & Richard Gardiner are listed as members of the Mercer Guild of London, Lord Mayor Sir Richard Gardiner serving as the guilds President.
Wyllyam Gardynyr (as his name was written in Welsh accounts) was born in 1451 in Oxfordshire. Granted title through his marriage to Helen Tudor, bastard daughter of Jaspar Tudor..
Battle of Market BosworthEdit
The Welsh accounts state that Sir William Gardner killed King Richard III with a pollaxe. The Welsh account reads, "Richard’s horse was trapped in the marsh where he was slain by one of Rhys Ap Thomas’ men, a commoner named Wyllyam Gardynyr."
The only dispute of this action is credited to English historians who stated that King Richard III was killed in battle with a pollaxe mistakenly by Rhys ap Thomas. Although it was Rhys ap Thomas' military prowess which led to the downfall of King Richard III's forces, it was indeed William Gardner who killed the last King of England to die on the battlefield].
King Richard III was the last King of the Plantagenet dynasty. Gardiner's actions would lead to his son becoming Lord Chancellor of England and the rise of his wife's family, the Tudors. Without his action, the modern monarchy under Elizabeth II would never have come to be. This is due to the fact that Henry VII is the great grandfather of James I, the direct ancestor of all the Kings and Queens following himself.
William Gardner, Gardiner, or Gardynyr, married Helen Tudor, born c. 1459, The illegitimate daughter of Jasper Tudor, 1st Duke of Bedford and 1st Earl of Pembroke, by one Mevanvy or Myvanwy ferch N (born Wales, died 1485), and lived at "the Bank" in Surrey, England. He lived his life as a cloth merchant.
- "Gardiner Generations & Relations, Vol. I" by Richard Thomas Gardiner
- "The Making of the Tudor Dynasty" by Roger Thomas