Kertag is a lean, medium-height human man with tawny skin, black hair worn short at the sides and longer on top, and a narrow face made expressive by sharp brows and a quick, crooked smile. He dresses in practical dark brown travel clothes beneath a well-kept leather jerkin, with a red thread bracelet tied around his left wrist by his grandmother. His most noticeable trait is the way he occupies very little space when entering a room, then gradually leans closer as though every conversation were a secret. His voice is normally low and clipped, but when rattled his breath catches between words and his sentences become unusually precise.

Kertag is observant, dryly funny, and unfailingly courteous to people who are ignored by polite society. He dislikes grand speeches but remembers tiny details about everyone he meets. He is generous in practical ways, repairing a broken lock, leaving food where a hungry family will find it, or quietly returning something stolen by a wealthier thief. He trusts competence more readily than kindness, though he wants very badly to be proven wrong.

Kertag Vezik was born in the Trades Ward of Waterdeep into a family whose members had been thieves, scouts, smugglers, and occasional informants for as long as anyone could remember. His grandmother taught him to read a room before he learned to read a book, while his father taught him the family trade by placing small objects in impossible hiding places and asking Kertag to find them. The Veziks did not steal from the hungry. Their rule was simple, take from the cruel, the careless, and anyone rich enough to make another person poor without noticing. Kertag learned the rule early, though he also learned that family rules could become excuses when coin was short. His first serious crime was a burglary arranged by an older cousin who planned to rob a widow of her savings. Kertag betrayed the job, hid the money beneath the widow's floorboards, and took the blame when the cousin discovered what he had done. The family cast him out for breaking their code of silence, but his grandmother secretly pressed her red thread bracelet into his hand before he left. Since then, Kertag has worked alone, choosing targets with care and using his inherited craft to protect people who cannot afford protection. He adventures now because Waterdeep's streets taught him that good intentions are not enough. Someone has to get through the locked door, find the hidden ledger, and put the stolen truth where ordinary people can reach it.