The Jewish Mobis a criminal organization which has only ever appeared in GTA IV. There is no clear/permanent Jewish Mob in GTA IV but the mob does shows up in two missions involving a diamond purchase gone wrong. They are led by Isaac Roth and his two lieutenants. Isaac Roth, one of the Hasidim, appears to be the boss of the operation, with Mori Green, a standard Orthodox Jew, as his right hand.
The LCPD database says that Roth, Green and The Jewish Mob in general do deals often with African warlord Claude Wome (who is an African diamond dealer dealing straight from Africa) in their deals, Wome imports blood diamonds directly from Africa to the Jewish Mob. Isaac Roth Is killed by Niko, under orders of Ray Boccino, in the mission ''Late Checkout''