Kull were especially large Urgals. Kull were born as Urgals, and through their growth, they grew progressively larger until they were above eight feet tall. They were then called Kull. This happened, according to Nar Garzhvog, because the 'Old Blood' flowed in their veins (possibly a sign of Atavism). However, Eragon observed that there seemed to be no link between the parents being a Kull and the child being a Kull. They could run for days without rest with endurance rivaling those of elves or even exceeding them, and were fast as horses (yet slower than elves). Kull lived for approximately sixty years, about the same as a human (as Eragon said that a human lives for about 60–70 years), but they were too heavy to ride horses.