Nick Shadow

“Devils have been pushing in on Voli territory for decades now. Someone summoned him inland in the deep forests, but he’s comin’ out to where there’s more souls to steal. He’s takin’ mortal form, and soon he’ll take over the whole city.”
Arlo Pisano, sheriff of the Lavalle District of Port Nabucco

Nick Shadow is a common name in folklore for the Archdevil Levistus, particularly in the urban legends of the Aquatic Kingdoms.

Summary

According to urban legend, Nick Shadow appears as a handsome, wealthy young man with a mysterious past, sometimes carrying epithets like "the Duke of Nowhere" or "the Rogue." He is sharp, quick-witted, charismatic, and intensely insightful. He offers hospitality to sellswords, adventurers, and thieves, inviting them to his home for a lavish dinner to discuss the possibility of a lucrative job. If they accept the job, he offers what appears at first glance to be a boilerplate contract; however, those with sharp eyes and a knowledge of Infernal may recognize the flourishes along the letterhead as additional clauses signing away the rights to their mortal Soul.
Those who sign contracts with Nick Shadow, whether aware of his true identity or not, are known as Shadow’s Army. He can appear at will to anyone who signs their true name to a contract and order them to do his bidding. If they refuse, more members of Shadow's Army will be tasked with stalking them and killing them if necessary.

Spread

Over time, the name "Nick Shadow" has been generalized as a name for any generic ne'er-do-well. It is often used as a tongue-in-cheek pseudonym by members of the underworld. Levistus himself has occasionally taken advantage of this, infiltrating thieves' guilds under this alias to gain trust and new members.
Fears of Nick Shadow, whether legitimate or fanned by rumor, have intermittently led to local panics and major crackdowns on crime. An interesting example of this occurred in Port Nabucco in the late 1050s to early 1070s. A rash of murders and attempted murders, primarily affecting wealthy citizens, was attributed to a shadowy figure known as "the Rogue." Despite her appearance as a petite, battle-scarred woman instead of an attractive man, rumors spread quickly that the Rogue was a new form of Nick Shadow. Over the next few years, a cult called the Shard of Shadow formed in response to this panic in an attempt to gain power and protection from the archdevil. This cult was successful in legitimately summoning Nick Shadow, who turned his attention on entrapping and murdering the easier lower-class targets of the city. The enhanced presence of the town guard disappeared as Nick Shadow bribed, corrupted, and even seduced many of its members. This continued until Y1071, when the newly formed Fiend's Bane finally banished Levistus and disbanded his cult.