RK Pachauri died at the age of 79 after a prolonged battle against heart illness.

Former TERI chief RK Pachauri died after a prolonged battle against heart illness at the Escorts Heart Institute in New Delhi on Thursday, a day after he was put on life support.

The 79-year-old environmentalist had earlier undergone an open heart surgery at the same hospital after suffering a stroke in Mexico last July.

TERI, short for New Delhi-based The Energy and Resources Institute, expressed "immense sadness" over Dr Pachauri's death. "The entire TERI family stands with the family of Dr Pachauri in this hour of grief," it said in a release issued soon after his death was reported.

"TERI is what it is because of Dr Pachauri's untiring perseverance. He played a pivotal role in growing this institution, and making it a premier global organisation in the sustainability space," said Dr Ajay Mathur, who succeeded Dr Pachauri as the TERI Director General in 2015.

Nitin Desai, chairman of TERI, described Dr Pachauri's contribution to global sustainable development as "unparalleled". "His leadership of the Intergovernmental Panel on Climate Change laid the ground for climate change conversations today," he said.

However, the world-renowned environmentalist's excellence in his field was overshadowed by a sexual harassment scandal involving a former woman colleague that culminated in his resignation from the prestigious institute in 2015. A Delhi court framed molestation charges against him in October 2018.

Dr Pachauri has consistently defended his innocence in the matter.