Ishan Thakur was Jagannath Mishras household servant. Only an eternal associate of the Supreme Lord could have the good fortune to render him personal service in his own home. The Lord accepts the service of his own confidential associates. When Mahaprabhu was born, Ishan had the chance to take the Lord on his lap and to hold him affectionately. He tolerated all of little Nimais childhood pranks and answered his every whim. Nimai was unable to go without Ishan for even a moment.
Ishan Thakur is counted as one of Chaitanya Mahaprabhus branches:
Srinath Mishra, Subhananda, Sri Rama, Ishan, Srinidhi, Sri Gopikanta, Bhagavan Mishra [were branches of Chaitanyas tree].
(Chaitanya Charitamrita 1.10.110)
How can I understand the activities of Ishan Thakur, whom Nimai used to lovingly call father? The son of Sachi, Nimai Chand, was his very life and Nimai would not go anywhere without him. In his childhood, Nimai was very naughty and he would make all kinds of capricious demands that Ishan would do his best to fulfill.
(Bhakti-ratnakara 12.95-7)
Ishan Thakur also had the chance to serve Nityananda Prabhu, Sri Chaitanya Mahaprabhus other self. Before the two sat down to eat in Sachis house, Ishan Thakur would bring water to wash their feet. The Lord would plea with his mother to be able to invite Nitai and when she finally agreed would go himself to invite him.
Ishan gave water for Gaura and Nitai to wash their feet and then they sat down to eat.
(Chaitanya Bhagavat 2.8.59)
As one of the Lords eternal associates, Ishan Thakur was fully aware of his divine nature. He knew that the worship of the devotee is more important than even the worship of the Lord himself. Thus he performed all kinds of service to Sachi Devi, who is none other than Yashoda Devi and was blessed by her affection. The Lord too blesses his devotees through his devotees merciful attitude. The Lords mercy follows upon the mercy of the devotee. Ishan Thakur glories are described in the work known as the Vaishnava-vandana:
vandiba ishana-dasa kara-joria kariThe Brahmin said, Look, here comes Ishan. What can I say, no one really understands his great qualifications. He has the reputation of knowing all the truths about the Lord, and he served Sachi by doing whatever she needed having done. Because he rendered such service to the Lords mother, Ishan is uniquely fortunate in the fourteen worlds. Even though I saw with my own eyes how much affection she had for him, I am unable to find the words to describe it."
shaci-thakurani yare sneha kaila variiI pay obeisances to Ishan Das with folded hands, for Sachi Thakurani was very affectionate towards him.
(Bhakti-ratnakara 12.94)
Ishan, most fortunate in the fourteen worlds, served the Lords mother constantly.
(Chaitanya Bhagavat 2.8.74)
When Mahaprabhu took sannyasa and left for Puri, Ishan was left with the responsibility of taking care of his mother Sachi and his wife Vishnupriya Devi and supervising their household. In his commentary to the Chaitanya Bhagavat (2.8.73), where it is said that Ishan Thakur did all the cleaning of the house, etc., Srila Bhaktisiddhanta Saraswati Goswami Thakur writes: Ishan was the servant in Mahaprabhus house. He gathered up the rice that had been thrown all over [by Nityananda] and made the house proper. There was no limit to Ishans good fortune. He was able to render service to the Lords mother throughout his entire life. Even after the Lord took sannyasa, he was engaged in the service of the Lords mother and his wife, showing the extent of the blessings he had received. He is therefore described as most blessed or the most fortunate amongst the blessed.
Ishan Thakur lived a very long life. He was still living even after the disappearance of Vishnupriya Devi and all the other devotees of Mahaprabhu in Nabadwip. Thus when Srinivas Acharya, Narottama Thakur and Ramachandra Kaviraj came to Nabadwip on pilgrimage, only Ishan was able to show them where all the places of the Lords pastimes were. In the Bhakti-ratnakara, it is said that when Ishan showed these devotees the holy places, they were already old and in a state of disrepair. This gives some idea of how old he must have been.
Nearly everyone has disappeared from Nabadwip. No one but the Lords servant Ishan remains here.
(Bhakti-ratnakara 11.721)
Srinivas Acharya, Narottama Thakur and Ramachandra Kaviraj received Ishan Thakurs blessings in Nabadwip Dham and were embraced by him before leaving to visit Srikhanda where they met with Raghunandan Thakur. When they arrived there, they received the news that Ishan had died.
I heard from some people while on my way here that Ishan has disappeared.
(Bhakti-ratnakara 13.21)
After Mahaprabhu and Sachi Mata had disappeared, Vamsivadanananda Thakur served Vishnupriya Devi and Ishan Thakur.
Other than this Ishan, there were several other associates of the Lord who had the same name. (1) Sanatan Goswamis servant was named Ishan. (2) There was a devotee in Vrindavan of that name. He is mentioned in the Bhakti-ratnakara as a member of the party of devotees who accompanied Rupa Goswami to the house of Vitthalesvara to have darshan of Govardhanadhari Gopal. He also is said to have blessed Srinivas Acharya, Narottama Das Thakur and Shyamananda Prabhu when they started their voyage to Bengal with the Goswamis books. (3) In the Gaudiya Vaisnava Abhidhana, there is mention of a certain Ishan Acharya who is identified as Vrajas Yauna Manjari. (4) The author of the Advaita-Prakasa was named Ishan Nagara.
[Excerpted from "Sri Chaitanya: His Life & Associates" by Srila Bhakti Ballabh Tirtha Maharaj]