I doubt there is a king or queen - especially in early history - who wasn't an utter bastard. That's how you play the Game of Thrones - you win or you die, etc, etc. George Martin is bang on with that.
It might be easier to pick out a non bastard. Ironically, the two most reviled Kings - John, and Richard III - are probably the only two who were slight but not total bastards. At least John bothered to learn English, which is more than Richard the Lionheart did.
Charles I was a total troll - marrying a French catholic, such a blatantly stupid thing to do and ended in the deaths of thousands and a civil war.
History is about way more than boring old kings and queens, though.
I'd go along with Thatcher (and most if not all of her cabinet) being amongst the most evil bastards in history. Ditto Cameron and Osbourne.
Sir Banastre Tarleton was actually nicknamed 'the Bastard' or 'Bloody Ban', I think. (British Commander in the American Revolutionary Wars, later politician). Hot, though:
upload.wikimedia.org/wikipedia/commons/0/05/Banastre-Tarleton-by-Joshua-Reynolds.jpg
Duke of Wellington always struck me as a bit of a twat. And such a snob, too. And brown-nosed the young Queen Victoria, shockingly. I much prefer Napoleon.
And going through the mists of time to my A Level History so this may be wrong... was it Lord Curzon (a Viceroy of India) who, seeing his estate's labourers swimming in a pond on his estate, expressed surprise that working class people weren't covered all over with hair, like monkeys?