Sir Thomas Malory, of Newbold Revel (Most likely) author of the "Morte d'Arthur", the second great recombination of Arthurian legend. (Geoffrey of Monmouth was the first; Alfred, Lord Tennyson was the third; T.H. White was the fourth - and drew heavily on Malory, and freely admitted it.)
He wasn't even on Geni at all until yesterday, which I found perplexing. So I went looking for possible relatives - and found his mother (Philippa Chetwynd), married to "unknown Malleore" and without listed offspring. (His father's name was John, and he had three sisters, of which so far I've found the name of one - Philippa, same as his mother's.)
So now Geni has all three candidates, including the dark-horse Thomas Mallory of Hutton Conyers (none of the experts think he's all that likely, because there are no records of him being a knight OR in prison).
Candidate #2, Thomas Malory of Papworth St. Agnes, was held under close supervision for much of his life, but there's no record of his ever being knighted - and with a son-in-law who was Norroy King at Arms, you'd think there would have been.
But Thomas Malory of Newbold Revel was definitely knighted, and committed acts which *justly* landed him in prison (robbery, conspiracy to commit assault, and something which was two separate counts of either outright rape or blatant adultery with another man's wife - the outraged husband chose to call it "rape"). Moreover, some of the places he was held (including the Tower of London, which was a Royal residence but also used for "guests the King needs to keep a very close eye on") had extensive libraries for the time, so he had something constructive to do with himself. Maybe prison reformed him to a certain extent (though he apparently remained a recusant Lancastrian in a Yorkist world), or at least made him reflect on the chivalric ideal and how few men - himself included - could live up to it. It's probably not an accident that the most sympathetic character in the Morte is Sir Lancelot, whose all too human flaws kept him from achieving the Grail.
I'm quite sure there are very many more British celebrities of this ilk that have not yet got profiles on Geni. Have you seen the Counties Projects? We are hoping that by adding famous people and historic people from each county we'll cover a wide range and hopefully draw in more British researchers.
We've got Geoffrey of Monmouth, but he's a "loose end" - no parents, no sibs, no connections. Since he was a monk, he's not likely to have left any descendants.
http://www.geni.com/family-tree/index/6000000000628865296