This is a challenge to create or post an NPC ne'er-do-well for all to share in. They can be a crime lord, or a criminal, a bounty hunter, smuggler, information broker, or whatever as long as they cruise the underworld. It can be a nemesis, rival, or minion group.
Along with stats, the NPC should have motivations, a specialty if they have one, the sort of locale they might be found in, an estimation of their resources, to whom they may be answerable to if they're just another link in the chain, and personality quirks.
As a bonus, you can offer some juicy story hooks that involve the NPC with the typical group of PCs.