The Athar are a faction in Sigil. The foundation of their philosophy is that the beings called gods — Zeus and Thor and Pelor and Mystra and Bahamut and all those entities worshipped all over the planes — are not worthy of worship.
Divine power, the Athar believe, comes from faith and conviction, and one need not worship a god to cultivate it - one can simply believe in one’s self, and power all the divine miracles of any cleric. The gods falsely claim monopoly over this power, and act like petty tyrants, with holy wars and fragile egos and totalitarian attitudes toward their worshipers.
The faction’s headquarters in Sigil is the Shattered Temple, in the Lower Ward, home to the Luminous Arbor, a tree that the Athar sacrifice magical items to.
Neon is a member of the Athar, who primarily works at taking down religious groups that get too big and prominent. They do this by leaking relevant information to local enforcers so they deal with them.
He was the sole person to leak information about a rising Asmodeus cult in Neverwinter, letting the Neverwinter guard bring them down.