A Daemonologist is a Warlock specializing in the arcane study and binding of Daemons. Whereas it is more than possible to embark upon a life of a Warlock and use Chaos Magic without any particular religious convictions, these wicked spell casters often become enamored with the whispered promises and many seductions of the Ruinous Powers. Offered power, knowledge and worse, these warlocks focus their arcane abilities towards the summoning and binding of Daemons. It is but a matter of time before even the strongest of these Daemonologists become ensnared in a web of contracts, agreements, oaths and unholy obligations.
Warlocks are not true Chaos Sorcerers, however. No Chaos God has chosen them, nor have they received a Mark of Chaos. To the arguably insane minds of such Sorcerers, Daemonologists are little more than puling weaklings, trafficking with all manner of minor Daemonic entities. Nevertheless, to ordinary folk, Daemonology is classed as one of the darkest of the dark arts. Even the lesser servants of the Ruinous Powers are a terrifying prospect to the peoples of the Empire.
Warhammer Fantasy RPG 2nd ED -- Realms of Sorcery (pg. 129-130)