Greatfather is by definition Strongest-of-the-Zuul. When the Player assumes his role, he becomes the motive force which directs all other Zuul in the Horde. All information and all power passes through Greatfather; he is an all-devouring maw to whom all the finest interrogators report, an all-powerful fist to whom all others bow, an all-powerful whip before whom all others cringe.
When Greatfather pays homage to the Suul'ka, however, he shapes himself and his coterie to reflect their glory. Each of the seven Suul'ka inspires a different transformation in Greatfather, as he struggles to embody the power that he reveres. By building an Altar and summoning one of the Great Masters, Greatfather submits himself and his people to the will of the Divine. His body, his mind and his followers are all shaped in the process.
Greatfather is also the custodian of the First Memory, that fragmentary vision of light, pain and dawning awareness which Zuul call the Forging. When Greatfather gathers a rally of thousands or millions of the privileged to his side, he is capable of re-broadcasting the memory of the Forging to all of them simultaneously, and they can all grasp feebly at what it was like for their forebears to be in the presence of the Great Masters, at the moment that they achieved full sapience.
The memory of the Forging is rescinded when Greatfather ceases to broadcast it, and the emotion left behind is a kind of Satanic bereavement and longing. Most Zuul males live in a state of spiritual pain which other races find very difficult to understand. The only Human equivalent is the Islamic conception of Hell: the damned of the Muslim world are deprived of the sight and presence of the Divine for all eternity, and Satan is the victim of the world's oldest and most painful divorce.
For the most part, the Suul'ka regard the Zuul with contempt or bemusement. They accept tribute and service as their due, and work alongside the Zuul for reasons that only they fully understand. Only He Who Shapes, known also as the Bloodweaver, regards the Zuul with special favor. As their Creator, He considers the Zuul an unexpected but delightful outcome to His experiments. At last He has sired a child who loves Him as He deserves!
Each of the Suul'ka change the Greatfather in different ways.
The Plaguefather follows the Bloodweaver.
The Warmonger follows the Kraken.
The Fathermother follows the Siren.
The Glutton follows the Cannibal.
The Hooded follows the Hidden.
The Faceless One follows the Deaf.
The Lich King follows the Eldest.