Thomsen of Trebond was the third child of Rispah Cooper and Coram Smythesson, the baron and baroness of Trebond after Thom of Trebond died. Thomsen had nine siblings: Jonthair, Alinna, Mylec, Daran, Liam, Thayine, Rose, Elenna, and Buran. He was a knight in the service of the Tortallan Crown and also served the kingdom in the King's Own. During the Scanran War Thomsen was still squire to Emeric of Legann, serving near the City of the Gods.
He didn't appear in any of the novels so far, but has only been mentioned by Tamora Pierce on the internet.