Answer: He read his obituary
Alfred Nobel was a Swedish inventor, chemist, engineer, and arms manufacturer — most notable in those roles as the inventor of dynamite. He was both a successful inventor and businessman, and maintained companies in multiple countries around the world, including those that manufactured the dynamite he invented, cannon balls and other munitions.
Alfred was deeply troubled by the obituary and saddened that the world would Remember him in such a fashion. In reaction to the obituary and out of a desire to associate his name with something positive, Alfred sets aside almost his entire estate to be used on his death to establish the Nobel Prizes in Physical Science, Chemistry, Physiology or Medical Science, Literature, and for those who furthered common good for humanity — most frequently referred to as the Nobel Peace Prize. His bid to improve the standing of his name was a success, and over a century later, the name Nobel is associated with the prizes he created.