First officer of the Apostles of the Eternal Glow, this evangelical off-shoot of the Church of Atom has plans to "Sweeten..." the wasteland by beckoning their followers to bathe in "Light." Gerard is direct and friendly to a point, but is also keen to further the church's causes, no matter what the cost. If Brother Gerard is ran into after a nearby nuclear explosion, the now radioactive shell of Megaton, he will be seen greeting all he meets with his new and terminally signed appearance, as the ultimate sign on his path to radioactive righteousness. 
If the Lone Wanderer has sabotaged Project Purity with President Eden's modified F.E.V., there will be a couple new dialogue options available when speaking with Brother Gerard. Gerard can be told that one can relate to "Tainting water under the guise of helping humanity," or express panic at the realization that they have just drunk F.E.V.-infected Aqua Pura.