Enthralled Wizard is an NPC Created by Bethesda for the quest: The Staff of Magnus during the College of Winterhold Questline, wherein there are Two Enthralled Wizard casting a barrier spell over the Dragon Priest: Morokei... Well now upon defeating Morokei, there is a spell tome on his body that teachs a Power (used once a day) that Creates an Enthralled Voiced Wizard... (Much like the Spectral Assassin Power, after the Dark Brotherhood Questline)... 

He will Follow you until he dies, and will cast spells in combat. 

This mod Also comes with a Summon Spectral Warhound, another npc created by Bethesda for the same quest. This is a lesser power, there is one spell tome located in the chest hidden in the water in the Room with Morokei, also the spelltome can be purchased at any Conjuration Vendor, as well as found in leveled chest throughout skyrim.