Karin (Katarina) Hansdotter (1539–1596) was the royal mistress of King John III of Sweden in the 1550s before his marriage during his time as Prince and Duke of Finland.
Karin is believed to be the daughter of Hans Klasson Kökkemäster, a former monk, which had been made priest in Stockholm after the reformation of 1527, and his wife Ingeborg Åkesdotter, a former nun and the illegitimate daughter of a nobleman. Her father was later fired from his work because of adultery. Karin was employed at the court of Queen Katarina Stenbock in the 1550s. John met her sometime in the middle of the 1550s, and she followed him to his fief in Finland where she was installed as his mistress (1556). In Finland, she lived openly as the hostess of Åbo Castle. In 1560, she and her children left for Sweden.
In 1561, before John's marriage to Catherine Jagellonica of Poland, Karin was married to Klas Andersson Westgöte (d. 1565), a servant (page) of John, and given the Wääksy Manor in Kangasala in Finland. She lost a lot of her property at John's rebellion against his half-brother, King Erik XIV, in 1563, but when John became king in 1568, he continued to support Karin and his illegitimate children.
Her first husband was murdered by King Eric during John's rebellion, but in 1572 she re-married, to a Lars Henrikson Hordeel (d. 1591). In 1576, Lars was ennobled by John on the condition that he take care of his issue with Karin. The same year, her daughter Sofia became a lady-in-waiting of Princess Elizabeth of Sweden, and in 1577, her children was ennobled. The same year, she became the neighbour of the deposed queen Karin Månsdotter, who was given the estate next to her. From 1580, Karin seems to have spent the majority of her time in Åbo.
Karin died in 1596 during the great Finnish peasant rebellion and did not have to witness the plundering of her estate; the rebellion reached her estate soon after her death.