Captain Thorpe is the commader of Dunavar's Spire. S/he signed an order for three golems which was carried by one of the artificers Beta used in his ambush of the party, these presumably being the three clay golems he used in said ambush. It is somewhat strange that a mere captain would authorise such a large order.
According to Word of Demonac (on the Discord), the party never investigated Captain Thorpe further, so the mystery will remain unsolved.