Ktetor () or ktitor (; ; ), meaning 'founder', is a title given in the Middle Ages in the Byzantine sphere to the provider of funds for construction or reconstruction of an Eastern Orthodox church or monastery, for the addition of icons, frescos, and other works of art. The Catholic equivalent of the term is donator. At the time of founding, the ktetor often issued typika, and was illustrated on frescoes ("ktetor portrait"). The female form is () or ktitoritsa ().
The donator or renovator of churches are known as "second ktetor" or "new ktetor" ().
The Serbian NemanjiÃÂ dynasty were ktetors to many monasteries and churches, including the "Medieval Monuments in Kosovo" inscribed as World Heritage.