NEW DELHI — India’s 11th president, A. P. J. Abdul Kalam, whose role in advancing India’s nuclear program made him one of his country’s most beloved figures, died on Monday after collapsing at an event where he was to deliver a lecture. He was 83.

The cause was cardiac arrest, doctors told NDTV, an Indian news channel.

Dr. Kalam, an ardent nationalist nicknamed “the missile man of India,” was embraced by both the left-leaning Indian National Congress party and the right-wing Bharatiya Janata Party. His death brought an outpouring of mourning on Monday from across the ideological spectrum at a time of intense political polarization in India.

Born into a humble South Indian family — his father rented a boat to fishermen working the strait between India and Sri Lanka — Dr. Kalam was singled out as a promising student and went on to study aeronautics.