Wulf and Ulf are completely identical twins. They are part of the Heron Brotherband and they are constantly arguing with each other, often about their appearance, which means they are constantly calling themselves ugly.
Wulf and Ulf are so identical, even their own mother cannot tell them apart. However, Ulf is older than Wulf. Hal, during Brotherband training, tied a rope around Wulf's wrist so he could tell them apart and he said, "Wulf has a wope on his wist". However, since Wulf and Ulf love to annoy others by switching identities, Wulf tied the rope on Ulf's wrist.
Little did Wulf know that this would later result in him being bear-hugged by Ingvar.
When they were building shelter for Brotherband training, Wulf and Ulf had to dig trenches to keep water away. They got into a fight about who's would hold more water, for Wulf's was deeper and Ulf's was wider. Hal grew infuriated and yelled that they would both hold the same amount of water. This was when he tied a rope around Wulf's "wrist".
Ulf and Wulf are the sail trimmers for the Herons, and when they are at sea, they are not allowed to argue. They are threatened by the prospect of Ingvar throwing them overboard. They took on identical scars against Zavac's crew on the forearm. In Arrida, Ulf takes on a massive knife wound to the side after his opponent had thrown down his weapons in Surrender. Ulf and Wulf could feel each other's feelings, and knew what the other was thinking about.
The twins rarely show affection, though in Scorpion Mountain, the readers will see a more sensitive and caring side from both twins.