The Fabricator Locum is a title given to a high ranking techpriest within the Martian Mechanicum, who serve as ruling deputy of a Forge World, subordinate to the Fabricator General. While most Forge Worlds have their own respective Fabricator-Generals and Fabricator-Locums, it is the Fabricator-Locum of Mars who serves as the de facto second in command of the entire Mechanicum after the Fabricator-General of the Red Planet itself.
- Zagreus Kane - Fabricator Locum of Mars during the Horus Heresy, later Fabricator General-in-Exile
- Trimejia Diadanei - Succeeded Kane as Fabricator Locum of Mars during the Horus Heresy
- Yuritus Omnicron - Fabricator-Locum of Esteban VII during the Horus Heresy.
- 1: Codex: Skitarii (7th Edition) (e-book), Strategic Disposition of a Forge World
- 2: Mechanicum (Novel) by Graham McNeill, Dramatis Personae
- 3: Codex: Skitarii (7th Edition) pg.13
- 4: Master of Mankind (Novel), Dramatis Personae
- 5: Adeptus Titanicus: The Defence of Ryza pg.19