The Avernic are one of the three demon races mentioned in Palkeera's memory. They were a slave race, described as primitive and tribal by the standard of Infernus. Three tribes of the Avernic are mentioned by Palkeera. These are the ruling Tsutsaroth, the physically largest of the three tribes, the Alyaroth, which were smaller but still had wings, and the Byzroth, the smallest of the three and lacking wings. Hellhounds are also known to be Avernic, but their true name is unknown..
Avernics were used as shock troops by the Chthonians, with each legion led by Chthonian nobles. Zaros tricked the Chthonian leader into giving him command of twelve such legions, which he took to Gielinor. There the Avernics found themselves among Zaros' elite, elevated into luxury by the vastness and skill of Zaros' human workforce.
The Avernics stationed in Gielinor began to harbour rebellious thoughts against their Chthonian leaders, who resided in distant luxury. Zamorak used this dissatisfaction to sway the Avernics to his side, including two Tsutsaroth who were willing to pledge their allegiance to him.
Zamorak kept his pledge, travelling with the Avernics to Infernus and waging war on the Chthonians. After twenty years the Chthonians had all been destroyed, with the few survivors banished to the Abyss. The Avernics were now their own rulers, and fiercely loyal to the one who'd brought this about. Some returned with him to Gielinor, where they formed the backbone of Zamorak's army during the God Wars. They were instrumental in the defeat of several desert cities, including Thammaron's destruction of Uzer, and Balfrug Kreeyath's attack on Ullek.
In the last days of the God Wars, K'ril Tsutsaroth was dispatched to seize a powerful weapon from Armadyl's Aviantese. The ensuing battle ended with K'ril and his bodyguards being frozen, along with the rest of the armies and generals present in the cavern.
In the Sixth Age, numerous Avernic still populate Gielinor. In addition to K'ril Tsutsaroth and his generals, who reside in the thawed-out battleground, adventurers may also encounter the Alyaroth, now known as black or greater demons, or the Byzroth, called lesser demons by Gielinorians. Hellhounds can also be found in many areas across Gielinor. Zamorak sent the Avernic twins, Avaryss, and Nymora to the Heart of Gielinor to claim it in his name.