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

Tenar's son, Spark, was a sickly child, who grew into a spoiled and disagreeable man. As an adult, he left the family farm and went to sea. After many years, his seagoing days come to an end when the ship he works on is disbanded for pirating. Thus he returns to his home, where he once again falls into the habit of expecting his mother to wait in him hand and foot.