Who is Spark from Tehanu: The Last Book of Earthsea and what is their importance?

Spark is Tenar's son. He was sickly as a child, and everyone thought he would die, thus, Tenar spoiled him when he was young. As a result, he became a disagreeable child, who refused to remain on the farm and longed to be a seaman. Spark left the farm and didn't return for a long period of time, a time that would have been longer had his ship not been disbanded by the king's men for piracy. Spark retuned to Oak Springs because he had nowhere else to go. Because of the laws of Gont, however, Spark is the rightful owner of the farm, and Tenar loses her position as the head of the farm when he arrives. He is described as cold and mean, expecting his mother to wait on him hand and foot upon. Tenar, on the other hand, is embarrassed by her son and jumps at the chance to leave the farm when she learns Moss is sick.