Surdas (Sant Kavi Surdas) was a 15th century blind saint, poet and musician, known for his devotional songs dedicated to Lord Krishna. Surdas is said to have written and composed a hundred thousand songs in his magnum opus the 'Sur Sagar' (Ocean of Melody), out of which only about 8,000 are extant. He is considered a saint and so also known as Sant Surdas, a name which literally means the "slave of melody".
...

Influence --
On Bhakti movement --
The philosophy of Surdas is a reflection of the times. He was very much immersed in the Bhakti movement that was sweeping North India. This movement represented a grass roots spiritual empowerment of the masses. The corresponding spiritual movement of the masses happened in South India in the first millennium A.D. but also started in 17 age

On the status of Brij Bhasha --
Surdas' poetry was a dialect of Hindi language, Brij Bhasha, until then considered to be a very plebeian language, as the prevalent literary languages were either Persian or Sanskrit. The works of Surdas immediately raised the status of Brij Bhasha from a crude language to that of a literary language of great repute.

Philosophy --- Shuddhadvaita --
Due to the training he received from his guru Vallabhacharya, Surdas was a proponent of the Shuddhadvaita school of Vaishnavism (also known as Pushti Marg). This philosophy is based upon the spiritual metaphor of the Radha-Krishna Rasleela (The celestial dance between Radha and Lord Krishna). It propagates the path of Grace of God rather than of merging in Him, which seems an extension of the belief of earlier saints like Kabir Das.

Foremost amongst the Ashta-chhaap Eight Disciples of the Master-Teacher Vallabhacharya are called the Ashta-chhaap, meaning, eight reprints (of the Master). Surdas is considered to be the foremost among them.