Despite having previously been staunchly loyal to his brother, Edward IV, Richard III has long had a reputation that's one of the blackest in our history. The youngest son of Richard, Duke of York and Cecily Neville, he was rumoured to have spent two years in his mothers womb before emerging with teeth, hair to his shoulders, and a humped back. Though it seems likely that he was born with deformities, it also seems that over the years these have been embellished and exaggerated, especially in light of his later reputation, with his perceived evilness of character being exhibited on his person by those writing of him (like Shakespeare, who's responsible for cementing this vision of Richard in the public consciousness via his play, Richard III).
Richard steadfastly supported his brother throughout the wars with the Lancasters (and is widely believed to have been involved in the murders of Prince Edward of Lancaster and Henry VI) and was therefore a natural choice for Protector of the young Edward V on the death of his father (especially as Edward IV's other brother, George, had been executed for plotting the King's demise and the rapaciousness of the Wydvilles, Prince Edward's maternal family, was notorious). However, Elizabeth Wydville clearly disagreed as she immediately spirited herself, her family (minus Edward, who was at the time under the care of his other uncle, Elizabeth's brother Lord Rivers) and quite a lot of the royal treasures to Westminster Abbey, where she claimed sanctuary. While it was apparent that Liz was trying to arrange for Edward to be kept under the control of her family and therefore retain the power she held as Queen, she also clearly feared the danger posed to her and her sons - fears which were justified as within three months Richard had declared his brother a bastard as well as a bigamist, disinheriting his lawful heirs and claiming the throne for himself.
Certainly it was widely believed in Richard's time (not just in England but throughout Europe) that he'd been the architect of their deaths and this along with other acts of tyranny (he appeared to have no time for legal niceties, executing some of his biggest opponents without trial) and the committing of both adultery and incest with his niece while his wife slowly died...
...saw even those who had previously supported him unite behind the Lancastrian heir Henry Tudor and invite him to claim the throne for himself. Which he did after Richard was killed during the Battle of Bosworth, marrying Richard's niece and former lover Elizabeth York, and thus bringing an end to the rivalry between the houses of Lancaster and York.
While not quite as insanely good as its sequel, The Princes In The Tower was yet again a deeply compelling, informative and rather convincing book seeking to illuminate one of the greatest 'unsolved' mysteries of the age, and I'm as eager as ever to devour every other book written by Weir.