Ruth Norman, alias Uriel, claims to have been Peter the Great of Russia, Maria Theresa of Austria and many other famous people. With this one exception, her notions are a collection of trite and derivative ideas--reincarnation, megalomania, extraterrestrial cultures of great power, strange scientific notions--common among crackpots for decades.
But there is one novel notion, which, if it is not born of simple ignorance, is worth investigation. It seems that Peter the Great died in 1725 and Maria Theresa was born in 1717. This is an overlap of eight years and she would have to have been two persons at the same time or be able to travel in time in some fashion. It would have been interesting to read of her explanations for either of these phenomena.