Not one but many mainly Chaitanya Mahaprabhu, Namadeva, Tukaram, Jayadeva
The Bhakti movement refers to the theistic devotional trend that emerged in medieval Hinduism and later revolutionised in Sikhism. It originated in the eighth-century Tamil south India (now parts of Tamil Nadu and Kerala), and spread northwards. It swept over east and north India from the 15th century onwards, reaching its zenith between the 15th and 17th century CE.
The leader of the bhakti movement focusing on the Lord as Rama was Ramananda. Very little is known about him, but he is believed to have lived in the first half of the 15th century. He taught that Lord Rama is the supreme Lord, and that salvation could be attained only through love for and devotion to him, and through the repetition of his sacred name.