Charles-Jean de La Vallée Poussin

Charles-Jean Étienne Gustave Nicolas, baron de La Vallée Poussin (French pronunciation: [ʃaʁl ʒɑ̃ etjɛn ɡystav nikɔla baʁɔ̃ də la vale pusɛ̃]; 14 August 1866 – 2 March 1962) was a Belgian mathematician. He is best known for proving the prime number theorem.