About 23 feet high
Karkus was the Gurg of the last known remaining giant colony on Earth. Karkus presided over the effective extinction of their species when his people began fighting and wiping each other out, and his people were forced to live (by wizards) in a dip beside a mountain lake between four extremely high mountains in Russia, leaving them no choice but to stick together for their own protection. Karkus was described as being twenty-three feet tall, the weight equivalent of a couple of bull elephants and having skin like rhino hide. He was a lazy giant who spent his days lying in the centre of a valley with his wife and waiting to be fed by the other giants.
In 1995, Rubeus Hagrid and Olympe Maxime, at Albus Dumbledore's request, journeyed to the colony to serve as envoys to the giants, in the hopes of making peace with them and securing their allegiance against Lord Voldemort and his Death Eaters, before Voldemort could convince them to join his side. After a month's trek, the envoys found them, and carefully approached Karkus the next day, identifying him as the Gurg because he was the biggest, ugliest and laziest, sitting there waiting to be brought food by the others, such as dead goats.
Karkus, at the time, was lying by the lake roaring at the others to feed him and his wife, when the envoys approached. Karkus received gifts of magic (which is favoured amongst his people), the first being a branch of Gubraithian Fire (or Everlasting Fire), bewitched by Dumbledore to burn forever more, which is something that not just any wizard can do. Hagrid proceeded to lie the branch down in the snow by Karkus's feet and said "A gift to the Gurg of the giants from Albus Dumbledore, who sends his respectful greetings". Karkus did not speak English, but knew enough to yell for a couple of giants who did and translated for them. Once he understood what it was, Karkus liked the present. Hagrid then told the very pleased Karkus that "Albus Dumbledore asks the Gurg to speak with his messenger when he returns tomorrow with another gift", and departed. He wanted to take things slowly so he didn't overload Karkus with information.
The following morning, Hagrid and Maxime returned, and Karkus was waiting for them, sitting up and looking eager. Karkus was then presented with a goblin-made, indestructible battle-helmet, and then sat down and talked with Hagrid and Maxime. Karkus and the other giants didn't talk much, but Karkus had heard of Dumbledore, and how he had argued against the killing of the last Giants in Britain, and seemed to be quite interested in what Dumbledore and Hagrid had to say. Hagrid and Maxime then departed, returning the next day with another gift; a roll of dragon skin.
However, that night a fight broke out between the giants, which happened quite often. Hagrid and Maxime could hear the fight from their cave, which according to them went on for hours and made an "unbelievable" noise. During this fight, Karkus was killed by another giant, Golgomath, and his head was ripped off and found lying at the bottom of the lake the next morning.
Karkus' name may reference his eventual status as a carcass, a dead body or corpse, at the hands of Golgomath.
- Harry Potter and the Order of the Phoenix (Mentioned only)