Mario Vargas Llosa, winner of the Nobel Prize in Literature in 2010, is said to write novels based on the premise that people have multiple personality. 

“El sueño del celta opens with an epigraph citing a text by the turn-of-the-century Uruguayan writer José Enrique Rodó, Motivos de Proteo:

‘Each one of us is, successively, not one but many. And these successive personalities that emerge one from the other tend to present the strangest, most astonishing contrasts among themselves.’

“This quote from Rodó is a kind of theory of human personality that appears in several of Vargas Llosa’s novels, but underlies in a consistent and significant way La casa verde, El paraíso en la otra esquina, Travesuras de la niña mala, and El sueño del celta” (1, pp. 110-111).

1. Raymond Leslie Williams. Mario Vargas Llosa: a life of writing. Austin, University of Texas Press, 2014.