Ven was a member of Species 6339, a race almost entirely assimilated by the Borg. Ven and his fellow crew members had introduced an artificial pathogen that attacked the Borg's vinculum. Seven of Nine was affected by this virus when USS Voyager passed near its location.
In 2375, Ven demanded that the vinculum taken by Voyager from a Borg debris field be returned so it could be used to inflict more damage on the Borg. Captain Janeway refused until Ven agreed to cooperate in curing Seven. (VOY: "Infinite Regress")