Former Indian president Abdul Kalam died on Monday after collapsing during a lecture in Shillong. He was 83.

Abdul Kalam served as president for five years from 2002. Kalam  was closely involved in the country’s civilian space programme and military missile development efforts, earning him the sobriquet  ‘India’s Missile Man’.  He worked as a scientist and science administrator, mainly at the Defence Research and Development Organisation (DRDO) and Indian Space Research Organisation (ISRO) before he became president. He also played a pivotal technical and political role in India’s Pokhran-II nuclear tests in 1998, shortly after the Atal Bihari Vajpayee government came to power. After his term, he returned to a life of education, writing, and public service. He received several prestigious awards, including the Bharat Ratna, India’s highest civilian honor.

“As president of India, Dr. Kalam was immensely popular and greatly admired. His warmth, humility and simple ways endeared him to one and all. He had a special love for children and sought to constantly inspire the youth of our country through motivational speeches and personal interaction,” President Pranab Mukherjee said.

“India mourns the loss of a great scientist, a wonderful President & above all an inspiring individual. My mind is filled with so many memories, so many interactions with him. Always marvelled at his intellect, learnt so much from him”, tweeted Prime Minister Narendra Modi.

Avul Pakir Jainulabdeen Abdul Kalam was born on 15 October 1931 in a poor Tamil Muslim family in Rameswaram. But he overcame all odds to study physics and aerospace engineering. After graduating from the Madras Institute of Technology (MIT – Chennai) in 1960, he joined DRDO as a scientist. He started his career by designing a small helicopter for the Indian Army. In 1969, Kalam was transferred to ISRO, where he was project director of India’s first indigenous Satellite Launch Vehicle (SLV-III) which successfully deployed the Rohini satellite in orbit. In the 1970s, Kalam also directed projects which sought to develop ballistic missiles from the technology of the successful SLV programme. He later became chief executive of the Integrated Guided Missile Development Programme which developed missiles like Agni and Prithvi.Kalam served as the chief scientific adviser to the Prime Minister and the secretary of the DRDO from July 1992 to December 1999 during which time Pokhran-II was conducted.