Weis" "Ancestral Roots. . ." (45:22), (110:23). As Count of Poitiers, William III. This was Duke William V, the Great, who reigned from 993 to 1030 and whose character seems to bear the imprint of that of his mother. He was married 3 times. He had a son named William by each of his wives. Each of the three Williams, in turn, became Duke of Aquitaine and Count of Poitiers.