The head of the Ramakrishna Math and Mission, Swami Atmasthananda, who was considered a mentor to Prime Minister Narendra Modi, died in Kolkata on Sunday. He was 98.

The spiritual leader had been ill since February 2015, PTI reported. A statement from the organisation said, “Despite the best medical attention, his condition deteriorated over the last few days and he passed away around 5.30 pm today at Ramakrishna Mission Seva Pratishthan hospital.” He will be cremated at the Belur Math on Monday.

Atmasthananda was born in present day Bangladesh and joined the order when he was 22. He was given the title of “swami” eight years later. He held various positions in the organisation, overseeing relief operations during natural calamities in India and its neighbouring countries. He was appointed president of the mission in 2007.

Prime Minister Narendra Modi called his death a “personal loss”. Modi had sought him out when he was posted in Rajkot and considered him his guru. Modi tweeted: “Swami Atmasthananda ji was blessed with immense knowledge & wisdom. Generations will remember his exemplary personality.”