With Chaitanya Mahaprabhu / Source

The four learned devotees in Lord Caitanya's pastimes, named

1. Kasinatha,


2. Lokanatha,


3. Srinatha, and


4. Ramanatha,

were incarnations of the four Kumaras. Of this there is no doubt. The names of these four devotees each end with the word 'natha', just as the names of the four Kumaras each end with the word 'kumara'. These four devotees became known as the 'four Nathas'.

Sri Rupa-manjari, who had been famous in Vrndavana-dhama, appeared as Srila Rupa Gosvami. Rupa-manjari's closest friend, who was known by the names Rati-manjari and Lavanga-manjari, appeared as Srila Sanatana Gosvami, who was honored by everyone, and who was considered to be like an extension of the transcendental body of Lord Caitanya Mahaprabhu. Sanatana Kumara, the jewel among the sages, entered the body of Sanatana Gosvami, who is therefore also considered to be an incarnation of Sanatana Kumara.

http://bvml.org/SCM/sggd.html
http://www.bvml.org/contemporary/witdbngs.htm