 In George R. R. Martin's A song of Ice and Fire series who plays the only viewpoint character to appear in every published book of the series?
Maisie Williams: Margaret Constance "Maisie" Williams (born 15 April 1997) is an English actress. Maisie Williams:  She made her professional acting debut as Arya Stark in the HBO fantasy television series "Game of Thrones" in 2011, for which she won the EWwy Award for Best Supporting Actress in a Drama, the Portal Award for Best Supporting Actress – Television and Best Young Actor, and the Saturn Award for Best Performance by a Younger Actor. Arya Stark:  She is a prominent point of view character in the novels, with the third most viewpoint chapters overall out of all the characters in the series so far, and is the only viewpoint character to appear in every published book of the series.
Margaret Constance "Maisie" Williams