The doctrine of Vishishtadvaita was propounded in eleventh century by:

Ramanuja, a Vaishnavite philosopher of the 11th-12th century from Tamil Nadu, propounded the doctrine of Vishishtadvaita (qualified non-dualism). This philosophy states that the soul, even when united with the Supreme God, retains its distinct identity. Basavanna founded the Lingayat/Virashaiva movement in Karnataka. Eknath was a Marathi saint of the Varkari tradition. Sakhubai was a devotee of Vithoba. Hence Ramanuja is the correct answer.