Former Indian President A.P.J. Abdul Kalam, who was known as the country's "Missile Man" for his engagement in the country's missile and nuclear development, died Monday after he collapsed during a lecture in Shillong, northeastern India, the Press Trust of India reported. He was 83.

He was rushed to a hospital after collapsing while delivering a lecture at the Indian Institute of Management at around 6:30 p.m., the news service said. The exact cause of his death remains unknown.

Serving as the 11th president from 2002 to 2007, Kalam was a popular head of state, rising from humble beginnings and eventually making contributions to the country in scientific projects.

He was born into a poor family in the southern state of Tamil Nadu in 1931. After studying aerospace engineering, he joined in the country's missile development programs from the early 1980s.

Kalam, a Muslim, served as an adviser in science and technology for a defense minister in the 1990s and played a pivotal role in the 1998 nuclear test by India.