Unnamed miller's wife

"She was a peasant girl. Pretty in a common sort of way. She was the miller's wife. Apparently they had married without my knowledge or consent. So I had him hanged and I took her beneath the tree where he was swaying. She fought me the whole time. She was lucky I didn't hang her, too. A year later she came to my gates with a squalling baby in her arms. A baby she claimed was mine. I nearly had her whipped and the child thrown in the river. But then I looked at you and I saw then what I see now. You are my son."

- Roose Bolton to Ramsay Snow

The unnamed miller's wife is a character mentioned in Season 5. She was the mother of Ramsay Bolton.

History
She a peasant woman married to an old miller. The miller did not obtain permission to marry again from his lord, Roose Bolton, so Roose rode out to the mill and hanged her husband off the branch of a nearby tree and violently raped her underneath her husband's swaying corpse. She became pregnant and gave birth to a son she named Ramsay. She arrives at the gates of the Dreadfort with Ramsay wanting Roose acknowledge him which he does upon noticing Ramsay's resemblance to himself after initially planning on whipping her and throwing the baby into the Weeping Water. She later died and Roose has her son legitimized by King Tommen Baratheon.

Season 3
Ramsay tells Theon Greyjoy that his mother tried to teach his kindness while his father taught him cruelty.

Season 5
Roose recounts to Ramsay his origins when Ramsay is upset over Roose's new wife Fat Walda Frey becomes pregnant and also to inspire him in their campaign against Stannis Baratheon to oust them from Winterfell.

Quotes
"My mother taught me not to throw stones at cripples, but my father taught me: aim for their head!"

- Ramsay Snow

In the books
Roose describes Ramsay's mother as ''“a girl not half [the old miller]'s age. She was a tall, willowy creature, very healthy-looking. Long legs and small firm breasts, like two ripe plums.”'' Roose sees her washing clothes in the Weeping Water while he is fox hunting and moment that he set eyes on her he wanted her and believes such was his due from the abolished the lord's right. Robert Glover says about Ramsay's origins, ''“The evil is in his blood. He is a bastard born of rape.” Roose admits to Catelyn Stark that Ramsay’s “blood is tainted, that cannot be denied.”''

She raises Ramsay at the mill. She often finds Ramsay to difficult to manage and repeatedly asks Roose to help her. Ramsay only moves into the Dreadfort upon the sudden death of Roose's trueborn son and heir Domeric.