Trojden, Duke of Redania and later Earl of Kovir, was the brother of King Radovid I. He founded the House of Trojden. As a young man, he was considered to be an extremely well connected, if somewhat of a slippery character. He was jealous and openly displayed his hatred for his brother.
So he was given the title of Earl of Kovir to basically get him out of Redania, and ideally as far away as possible. Officially hi was a vassal king of Redania, but he was not obliged to pay tribute, his only obligation was to do "no harm".