Thelvis Hollrig was a leaguesman who presided over the Sky Shipyards of Undertown. Wind Jackal did a deal with him in order to pay for repairs to the Galerider. Under the terms of the agreement, Wind Jackal would deliver a shipment of bloodoak timber to the Sky Shipyards, and Thelvis Hollrig would write off the costs of the repairs.
When Quint returned with the bloodoak timber, Thelvis Hollrig fed him information that the Leagues of Undertown were planning to unite and attack the sky pirates. This act was performed under the orders of the Leaguesmasters, who intended for the sky pirates to swoop into the battle confidently, only to be defeated by their secret weapon, the Bringer of Doom. Quint notified the sky pirates at Wilderness Lair of Thelvis Hollrig's information on the Leagues' movements, and the leaguesmen attacked, but the sky pirates ultimately won the battle when the Bringer of Doom crashed. Nobody knows what happened to him afterwards