The most unusual feature of these giant-sized, humanoid, bipedal creatures was the extra arm growing out of their chest. They had large, curved tusks on either side of a wide mouth, relatively small eyes and nose for the size of their head, and one ear that was significantly bigger than the other. An adult stood about eighteen feet (five and a half meters) tall and weighed about 4,500 pounds (2,000 kilograms). Their stench was quite strong, because they seldom bathed.
Athachs loved to eat and collect gems and jewelry. They spent hours polishing the bracelets on their fingers, necklaces on their wrists, and other shiny acquisitions. They enjoyed smashing things with their crude morningstars and did not shy away from fights with creatures smaller than themselves. They feared giants and other creatures their size but had a particular hatred for hill giants, whom they attacked on sight if the odds were in their favor.
Athachs preferred melee combat with multiple morningstars but would throw rocks if that was not a good option. They tended to go on the offensive immediately, wading in and swinging their weapons indiscriminately at anything in their long reach. Sometimes, they would rush through a heavily armored front line to get to the more squishy targets in the rear. Anyone who hurt an athach enough to get its attention was a prime candidate for a poisonous bite from its big mouth and tusks.
Athacs spoke a pidgin form of giantish, but they hated hill giants and feared the other species of giants. Athachs could be found living in tribes of up to a dozen members but also marauded in gangs of two to four or went solo.
Around the Year of Wild Magic, 1372 DR, there were two atypical athachs, named Horokh and Beelbraeth, working at the Moonwyvern Inn near Silverymoon. They were loyal to the proprietress, Clarshee Taraghe, spoke Common, and loved to cook. They both had long, shaggy fur to protect them from the northern winters and three horns on their heads.
- Skip Williams, Jonathan Tweet, Monte Cook (July 2003). Monster Manual v.3.5. (Wizards of the Coast), p. 21. ISBN 0-7869-2893-X.
- Richard Baker, Matt Forbeck, Sean K. Reynolds (May 2003). Unapproachable East. (Wizards of the Coast), p. 152. ISBN 0-7869-2881-6.
- Ed Greenwood (October 2001). “Elminster's Guide to the Realms: The Moonwyvern Inn”. In Jesse Decker ed. Dragon #288 (Wizards of the Coast), pp. 74–75.