Yuri Vladimirovič Matiyasevich (also spelled Jurij/Yurij/Yurii Matijasevič/Matijasevich/Matiasevich, Russian Ю́рий Влади́мирович Матиясе́вич) is a Russian mathematician who obtained a negative solution to Hilbert's tenth problem. By a seminal theorem of Matiyasevich, for every statement in mathematics (say ZF set theory) there is a Diophantine equation? whose solvability is equivalent to the validity of the statement. This is not of much practical importance, but of large theoretical importance.
An accessible presentation of Matiyasevich’s theorem is in