Baron Klaus Eriksson Fleming (Swedish: Clas Eriksson Fleming; 1535 in Pargas – 13 April 1597 in Pohja)[3] was a Finnish-born member of the Swedish nobility and admiral, who played an important role in Finnish and Swedish history during the rise of Sweden as a Great Power.

He was a strong supporter of the legitimate king of Sweden and Poland, Sigismund Vasa, and therefore an enemy of Sigismund's paternal uncle, duke Charles of Sudermania, who had also laid claim to the Swedish throne.

[4] His sister Filippa Fleming (d. 1578) wrote a will which disinherited him for his abandonment of her during a long illness, bequeathing Yläne manor to John III of Sweden, her estates in Sweden proper to her niece Anna Fleming, and her remaining estates to her betrothed, Knut Jönsson Kurck.

[5] While his fleet was being prepared at Siuntio in April 1597, he suddenly fell sick.

Nevertheless choosing to travel to meet his wife at Perniö, he died somewhere near the church of Pohja during the night of 12-13 April.