The Myth

The Katthveli (“Cat-whale”) is one of Iceland’s legendary illhveli, or evil whales. Smaller than many of its monstrous relatives, it is nevertheless feared by sailors. It is said that merely speaking its name while at sea will attract the creature.

The Katthveli has the body of a small whale, dolphin, or seal with a broad front and narrower hindquarters. It has the face of a leopard, long whiskers like a cat, hooked claws on its flippers, gleaming eyes, and short tusk-like teeth. When calm it purrs as it exhales, but when angered it mews, hisses, and spits like a furious cat.

The creature is notorious for attacking boats. It swims beneath vessels to overturn them, rams their hulls, or follows ships for hours, preventing fishermen from working. One tale tells of a Katthveli that thrust its head through the side of a boat, while another describes one rearing from the sea, placing its flippers over a boat’s gunwale, hissing and snapping at the crew until a sailor fired a gun into its mouth.

A famous legend tells of Saint Brendan, who encountered a tame sea-cat that had been raised by pilgrims on an island. As it grew larger and more ravenous, it devoured all but one of its caretakers. Brendan prayed for deliverance, whereupon a gigantic whale rose from the sea, seized the monstrous sea-cat, and dragged it into the depths, where both creatures drowned.

Tradition / Region: Icelandic Mythology
Alternative Name: –
Category: Whale, Cow

The Myth

The Nauthveli, also called the Ox-Whale, is one of Iceland’s feared illhveli (“evil whales”) and is said to be the second largest of these monstrous sea creatures. Like the other evil whales, it is considered inedible, and tradition warns that merely speaking its name aloud can summon it.

The Nauthveli is a massive toothed whale with a black-and-white body resembling a cow. Its enormous head resembles that of a bull, bearing two large nodules, while its long body narrows into a worm-like tail without fins.

Its most terrifying feature is its voice. When hungry, the Nauthveli lets out an immense bull-like bellow that echoes across the sea and coastline. The sound resembles the roar of enraged cattle and can be heard over great distances. Its vibrations shake the ground and are powerful enough to knock oars from sailors’ hands. Whenever its bellow is heard, people refuse to sail.

Like all evil whales, the Nauthveli attacks boats and delights in killing people, but it has a particular craving for cattle. Its supernatural bellow hypnotizes cows and bulls, compelling them to run over cliffs and plunge into the sea. Once they reach the water, the whale toys with them like a cat playing with a mouse before biting them in half and devouring them.

The creature is also drawn to cattle carried aboard ships. One legend tells of a Nauthveli that relentlessly pursued a vessel near Grímsey until the sailors released the single cow they were transporting. The animal immediately leapt into the sea, satisfying the monster.

After the Nauthveli has been heard, cattle are traditionally kept locked away for several days until its enchantment fades. In areas where the monster was believed to roam, herding cattle near the coast was discouraged. According to tradition, sacrificing a single bull or cow would appease the Nauthveli, making the sea safe once more.

Sources

Wikipedia contributors. (n.d.). Fylgja. In Wikipedia. Retrieved June 29, 2026, from https://en.wikipedia.org/wiki/Fylgja