[Taqwus]

1. Make sure there's at least Death-3 on your pretender if you're playing Ashen Empire; probably Death-5 for Soul Gate.
2. Select him.
3. Check the list of spells he can cast. These will include spells for summoning mages (Spectators, Dusk Elders) and priests (for Ashen Empire -- Archbishops, Bishops, Acolytes; for Soul Gate, Wraith Consuls, Shadow Tribunes etc).
A Dusk Elder, for instance, is a death-3/random-1 mage. An Archbishop is an Unholy-4 priest. Both cost a lot of death gems so you won't be summoning them very quickly in the beginning.