|ATTENTION! SPOILERS AHEAD!!|
This article contains information from later episodes of The Magnus Archives and may contain major spoilers for the setting and plot. Continue at your own risk.
Callum Brodie is implied to be the son of Philip Brown and Caroline Brodie. Manuela Dominguez mentions that his father had been "directly marked by the Dark" and Philip had an encounter with The Dark in HMP Wakefield, where Robert Montauk was imprisoned. In 2004, Caroline left Philip because he became abusive and an alcoholic.
In 2017, Callum was kidnapped by The People's Church of the Divine Host where they attempted to use him as a vessel for Maxwell Rayner. This failed because of intervention from Basira Hussain and other Section 31 officers.
As of episode 173, he presided over a domain of the Dark, where he terrorised younger children by planting the idea of monsters chasing them and letting their imaginations do the rest. Before The Change, he forced kids younger than him into dark closets, forcing them to experience the fear he felt when captured by Rayner.