Colstan was second-in-command of the Hand, the snatch-and-grab kidnapping agents of the Eye. He prided himself knowing by sight all the major players in Waterdhavian politics, though not necessarily the most famous. His main hobby was the uncovering identities of the Lords of Waterdeep. He managed to identify Brianne Byndraeth, a revelation that was very useful for his fellow Xanathar agent, Randulaith.
He usually sent hireswords to start a brawl or similar incident with all new adventurers in the city, in order to steal their belongings and get them captured by the Hand.
Colstan was a patient, calculating schemer who avoided personal danger whenever he can, preferring to work at a distance through hired knives and behind-the-scenes manipulation.