Stranger (the Seven)
The Stranger is one of the seven aspects of a single deity. Believers of the Faith of the Seven consider that God is one with seven aspects, as the sept is a single building, with seven walls.  He rides a pale mare. In his appearence he shares similarities with the real world imaginations of the death as the "Grim reaper" or "Angel of death" with a face like a skull.
An exception to the other aspects, the Stranger represents death and the unknown. The Stranger is neither male nor female, yet both, ever the outcast, the wanderer from far places, less and more than human, unknown and unknowable.  The Stranger's face has also been described as half-human, concealed beneath a hooded mantle.
Worshippers rarely seek favor from the Stranger, but outcasts sometimes associate themselves with this aspect of God.
Silent Sisters are sometimes referred to as 'Wives of the Stranger'. They clothe themselves in grey and keep their faces cowled except for their eyes.
The House of Black and White contains a public shrine with idols of many death gods, including the Stranger.
A Clash of Kings
Catelyn Stark prays in a nameless village’s sept. The sept is modest and has no statues of the Seven, only rough charcoal drawings to represent them. Here the Stranger's face is a black oval, a shadow with stars for eyes. It makes Catelyn uneasy. She thinks to herself that she would get scant comfort there. 
Upon entering the sept of Maegor's Holdfast, on the eve of battle Sansa Stark sees that there are even a few candle flames dancing below the Stranger’s half-human face. Sansa visits each of the Seven in turn, lighting a candle at each altar.
A Feast for Crows
During a meeting with the small council Cersei that promises that before she is done with Sansa Stark she will be “singing to the Stranger, begging for his kiss”  During the same meeting Cersei thinks to herself that one day she must light a candle to the Stranger for carrying Renly off and leaving Stannis. If it had been the other way around her life would have been harder.
A Dance with Dragons
During her confinement Cersei prays until her knees are raw and bloody, until her tongue feels thick and heavy. She prays to all the aspects of the godhead, even the Stranger.
The Winds of Winter
As the Second Siege of Meereen is beginning Tyrion Lannister thinks to himself that the Stranger has mounted his pale mare and is riding toward them with his sword in hand, but Tyrion does not care to meet with him again. Not now. Not yet. Not this day.
Any god in a storm.
- Cersei Lannister, on praying to the Stranger
That's the Stranger coming, Penny.