Karin Månsdotter (in English Catherine; 6 November 1550 – 13 September 1612) was first the mistress and then the queen consort of King Erik XIV of Sweden.

According to legend, Erik XIV first noticed her selling nuts at a square in Stockholm, and was so astonished by her beauty that he took her to court as his lover, a story mentioned by Dorothea Ostrelska[1] In reality, however, Karin Månsdotter was in 1564 employed as a servant to Karin, wife of the king's trusted court musician Gert Cantor,[1] who held a tavern and a guest house in his home, and likely served their guests as a waitress.

[1] The royal accounts states that she was given a new and expensive wardrobe and her own staff, among them her own former employer: Karin, the wife of Gert Cantor.

[1] Before this the king had several mistresses in parallel, such as Agda Persdotter and Doredi Valentinsdotter, but when Karin entered his life, he dismissed them all.

According to chronicler Daniel Hund, he was in fact trapped by Erik, who had asked Karin to send for him.

She was described as very beautiful with long blond hair and innocent eyes, and her personality seems to have been calm, humble and natural.

The king was mentally unstable, and she seems to have been the only one who could comfort him and calm him down, which made her appreciated by his relatives, who considered her good for him.

[1] Karin is reported to have been a good friend of Persson's wife Anna Andersdotter, who apparently often accompanied her on her travels between the different royal palaces.

It is unknown whether Karin Månsdotter had any political influence, but a popular image in Swedish history was of her serving as a counterweight to Jöran Persson; a painting by Georg von Rosen three hundred years later (1871) illustrates this, showing the king on the floor, confused by his inner demons, with Karin Månsdotter at one side holding his hand, looking like an innocent angel giving him strength to resist the demands of Jöran Persson, standing on the other side of him, trying to get him to sign a document.

Countess Märta Sture, sister of the former queen Margaret Leijonhufvud, appealed to Karin Månsdotter for the prisoners' protection.

[1] Later the same morning, the king visited Svante Sture in prison, fell on his knees before him and begged for his friendship.

Karin Månsdotter was walked to the altar by the king's cousin Per Brahe under a banner of golden textile carried by four nobles.

[1] During the coronation, Lord Chancellor Nils Gyllenstierna fainted and dropped the crown he was carrying to the floor.

During her period as queen, Karin gave gifts to her friends and relatives, such as Anna Nilsdotter i Hammarstorp, who has been identified as her sister despite her different patronymicon, her paternal cousins in Sko kloster, and her "Fränka" (meaning "female relative") Anna Eriksdotter i Sko.

Shortly after they were imprisoned, their children were placed in the care of Catherine Stenbock and their French governess Johanna (Jeanne) de Herboville, but were reunited with their parents in 1570.

[1] Queen Karin and her children were separated from her husband on 14 June 1573 to prevent the birth of any more legitimate offspring.

[1] Karin and her children were taken to the Castle of Turku (Åbo) in Finland, where she remained under house arrest until the death of her husband four years later.

She was treated with kindness and given the royal estate Liuksiala Manor in Kangasala, Finland, where she lived the rest of her life.

Karin became respected and liked in Finland; during the great peasant rebellion (Cudgel War) in 1596–97, the rebels refrained from plundering her estate.

Her daughter, whose spouse had been loyal to King Sigismund, was forced to flee from Charles IX to Riga in 1598, but when she returned in 1603, Karin gave her refuge.

In August 1605, Charles IX gave instructions that Karin and her niece (her sister's daughter, who was apparently staying with her) be moved to Stockholm.