Srila Gaura Kishora Dasa Babaji Maharaja is the spiritual master of Srila Bhaktisiddhanta Sarasvati Gosvami Prabhupada.

namo gaura-kisoraya saksad-vairagya-murtaye
vipralambha-rasambhode padambujaya te namah

I offer my respectful obeisances unto Gaura-kisora dasa Babaji Maharaja [the spiritual master of Srila Bhaktisiddhanta Sarasvati], who is renunciation personified. He is always merged in a feeling of separation and intense love of Krsna.

From Srila Prabhupada’s letter:

“Yes, there are examples of Krsna conscious persons whose worship was solitary life, and the greatest example is Haridas Thakur. Haridas Thakur used to live only in a cave sometimes and would spend his whole time chanting the Hare Krishna mantra.

“Similarly, Gour Kishore das Babaji, the spiritual master of my guru maharaj, would chant alone in a solitary place so as not to be bothered by anyone in his meditation on Krishna.

“But these great personalities are not to be imitated. If we artificially imitate, out of some negative feeling or out of desire for adoration as a saintly person, it will not be very beneficial.”