The correct answer is option 'C': Shankaracharya.

The Bhakti movement was a significant socio-religious movement that emerged in medieval India. It aimed to promote devotion and personal connection with a chosen deity or god, emphasizing the importance of individual religious experience over ritualistic practices. The movement gained prominence between the 12th and 17th centuries and had a profound impact on Indian society, culture, and religious practices.

Shankaracharya, also known as Adi Shankara, is considered one of the key figures in the development of the Bhakti movement. He lived in the 8th century CE and was a philosopher and theologian who played a crucial role in the revival of Hinduism. Shankaracharya's teachings and commentaries on ancient Hindu scriptures, particularly the Vedas and Upanishads, laid the foundation for the Advaita Vedanta philosophy.

Shankaracharya's Contribution to the Bhakti Movement:

1. Advaita Vedanta Philosophy: Shankaracharya's teachings emphasized the concept of Advaita (non-dualism), which posits that the individual soul (Atman) and the universal soul (Brahman) are essentially the same. This philosophy provided a philosophical basis for the Bhakti movement and influenced subsequent Bhakti saints.

2. Synthesis of Bhakti and Jnana: Shankaracharya emphasized the importance of both devotion (bhakti) and knowledge (jnana) in attaining spiritual liberation. He believed that devotion and knowledge were not mutually exclusive but rather complemented each other. This integration of bhakti and jnana became a fundamental principle of the Bhakti movement.

3. Reinterpretation of Hindu Scriptures: Shankaracharya's commentaries on ancient texts aimed to reinterpret and revive the essence of Hindu scriptures. He emphasized the non-dualistic nature of the divine and the individual, encouraging individuals to develop a personal connection with their chosen deity.

4. Establishment of Mathas: Shankaracharya is also credited with establishing four mathas (monastic institutions) in different regions of India. These mathas became centers of learning and spiritual guidance, promoting the teachings of Advaita Vedanta and providing a platform for the propagation of the Bhakti movement.

In conclusion, Shankaracharya's philosophical teachings, emphasis on the synthesis of bhakti and jnana, reinterpretation of Hindu scriptures, and establishment of mathas played a crucial role in laying the foundation for the Bhakti movement in medieval India. His contributions helped shape the movement's core principles and paved the way for subsequent Bhakti saints to spread devotional practices throughout the country.