Tyranny of Dragons
Most of a vampire’s victims become vampire spawn-ravenous creatures with avampire’s hunger for blood, but under the control of the vampire that created them. If a true vampire allows a spawn to draw blood from its own body, the spawn transforms into a true vampire no longer under its master’s control. Few vampires are willing to relinquishtheir control in this manner. Vampire spawn becomefree-willed when their creator dies.