It was probably an active predator, hunting with the large sickle-shaped claw on the second toe of each foot. It was a large dromaeosaurid: the first and only individual specimen found is estimated at being 5 meters (17 feet) long. The name comes from Achilles, a famous ancient Greek warrior of the Trojan War. It refers to the large Achilles tendon needed to use the sickle claw on the foot, which was the major weapon of dromaeosaurids. The one species is named "A. giganticus" because it is much larger than other dromaeosaurids.