Volkmar the Grim, Grand Theogonist

All the rules that normally apply to an Empire Warrior Priest also apply to the Theogonist (see page 16 of the Empire Book), with the exception that his Prayers of Sigmar have a Power Level of 4.

Warrior Priests are granted exceptional powers by their divine patron. Not as powerful as the spells of the Battle Wizards, these Prayers are still very valuable on the battlefield.
Once per Empire Magic phase, a Warrior Priest is allowed to use ONE prayer chosen from the Prayers of Sigmar list. Prayers are cast exactly like Bound spells from magic items, with a Power Level of 3. They can be cast on the Priest himself or on any one character or unit champion within 12" of the Priest. Prayers never affect a model's steed, and cannot be cast on Knights of the White Wolf or their Grand Master. Note that a Warrior Priest is never considered to be a Wizard.

Warrior Priests and the unit they are with bate all models in any of the following armies: all Chaos (Chaos Warriors, Beastmen, Daemons and Chaos Dwarfs), all Undead (Kltemri and Vampire Counts). all Skaven.
Note that this power does not affect other characters (they are more difficult to influence than the average soldier) and units Immune to Psychology are not affected by this power as well. Also note that Warrior Priests will never join units of warriors who are not devout to Sigmar, so they cannot join units of Knights of the White Wolf