Kosoy, Kosoi or Cosoi ( meaning slanting, oblique, etc.) is a Russian masculine surname, its feminine counterpart is Kosaya. It may refer to Feodosy Kosoy (fl. 1550s), Russian serf-monk Stewart Kosoy (1950–2015), American video game designer Vasily Kosoy (1421–1448), Grand Prince of Moscow Vassian Patrikeyev (Vassian Kosoy), Russian ecclesiastic and political figure and writer