Who was the brother of XXX?
Marcel Riesz
Marcel Riesz (Hungarian: Riesz Marcell, pronounced (ˈriːs ˈmɒrt͡sɛlː); 16 November 1886 -- 4 September 1969) was a Hungarian-born mathematician, known for work on summation methods, potential theory, and other parts of analysis, as well as number theory, partial differential equations, and Clifford algebras.