The AMS news page reports that the Norwegian mathematician Atle Selberg passed away on August 6. As the AMS news item states, Selberg is perhaps best known for his work on the zeros of the Riemann zeta function, for which he was awarded a Fields Medal in 1950, and for his "elementary" proof of the prime number theorem. His honors include the 1986 Wolf Prize in Mathematics.
Selberg was also involved in one of the most famous controversies regarding allocation of credit for a result. His controversy with Paul Erdös regarding the genesis of the "elementary" proof of the prime number theorem features in every account of Erdös' life and work. See, e.g., this book and this obituary.
Addendum: I just saw that Luca Trevisan also has a (better) post on Selberg's death. Luca points to an obituary on the IAS web pages.