Gidim are created at the time of burial, taking on the memory and personality of the decedent.
The Gidim come to the Underworld and are judged by the quality of their burial and the number of people who remember them. People with lots of children have a clear advantage over those with less or no direct offspring at all. For the quality of the afterlife, it is also very important to have a proper grave that is looked after by the family and regularly watered. This is necessary as, for the Gidim, Irkalla is a horribly dry and dusty place and the only relief comes from the charity of their descendants.
Under special circulmstances, Gidim leave Irkalla and come back to Earth, sometimes to provide the humans with their prophecies, sometimes to take their last revenge and seize their killers.