Jonathair of Trebond was the oldest child of Rispah Cooper and Coram Smythesson, the baron and baroness of Trebond after Thom of Trebond died. Jonthair had nine younger siblings: Alinna, Thomsen, Mylec, Daran, Liam, Thayine, Rose, Elenna, and Buran. He was a knight in the service of the Tortallan Crown and probably his father's heir to the barony. He also served in the Scanran War as a knight.
He didn't appear in any of the novels so far, but has only been mentioned by Tamora Pierce on the internet.