The Burning Prince
The igris was a dangerous species of humanoids. They were eight feet tall, with massive claws and sabre teeth. They were impervious to nearly all weapons and could break through anything except a forcewall.
These creatures were once people transformed through experiments by the Drashani Empire in order to make a slave labor force. They were created by distilling away a person’s higher brain functions and hurling their psyche into another dimension known as the Undervoid. In their place, their old bodies would be transformed into igris while their minds remained trapped in the Undervoid. Tenebris discovered a way to quickly transform large numbers of people into igris through use of a weapon known as the Acheron Pulse, which weaponized his psychic abilities to transform entire planets full of people into igris at once, at which point he would retrieve their psyches and place them back into their bodies, transofrming them into Wrath. (The Acheron Pulse)
During the civil war between the Houses of Gadarel and Sorsha, the igris took over the planet Sharnax. After Princess Aliona of Gadarel crashed on Sharnax, an igris was captured and studied by Sorsha in order to find a way to fight them during the rescue. The igris was held on the rescue ship and was let free by a system failure. Theigris killed most of the crew and was only killed when a hole was blasted in the ship by Captain Shira, causing it to crash on Sharnax as well. (The Burning Prince)