Ren Grouver was a dwarf and member of the Scoia'tael who worked for Yaevinn.
He can be found in the Vizima sewers of the Trade Quarter, if you get the Echoes of Yesterday quest and you will meet him again at the bank during the Gold Rush quest.
If Geralt attacks the Scoia'tael during Gold Rush: He and the Scoia'tael robbers were killed by Geralt.