Red Priestess (High Sparrow)

"Lord cast your light upon us. For the night is dark and full of terrors. I was once as you are now. Bought and sold, scourged and branded. [...] The Lord of Light hears your voice. He hears the king as he hears the slave; he hears the Stone Men in their misery. [...] He has sent you a savior! From the fire she was reborn to remake the world! The Dragon Queen!"

- The Red Priestess preaches of Daenerys Targaryen to a group of slaves

A Red Priestess is a minor character in the fifth season. She is portrayed by Rila Fukushima.

Background
This woman was a slave of apparently eastern origin. According to the Volantene tattoo on her face, she was trained as a prostitute. It seems that she was eventually bought by the Red Temple in Volantis and was trained as a Red Priest.

Season 5
At the Long Bridge, she preaches to the slaves gathered around her that Daenerys Targaryen is a prophesied savior sent by R'hllor. Tyrion Lannister and Varys watch and listen from a distance, with Tyrion mocking her until the priestess turns to him and stares at him intently.

In the books
In the books, a male Red Priest in Selhorys, a town under Volantene rule, plays the same role. Benerro, the High Priest of R'hllor at the Red Temple in Volantis, preaches a similar message in Volantis itself, very much like the Red Priestess.

In the novels, slaves bought by the Red Temple of Volantis are branded with tattoos in the shape of flames, be them Red Priests, temple guards - known as the Fiery Hand -, or temple prostitutes.