The followers of the mechanogod Whrrrm, those who could never have come about until the advent of steamtech.
And because they had shown they could not be trusted, Iev abolished the use of Kren save by those few individuals he trusted.
~The True History of the Order, by F’ian circa 300 AW
In addition to the Thieves' Guilds, there is a hierarchy that all thieves are part of. Rank is based on skill, and can be raised or lowered at any time. The Queen of Thieves, the greatest living thief in the world, is the ruler. Guildmasters answer only to her, and she answers to no one at all.