Irkens, also known as Til'uni Ko'en by the Second Human Empire and Annoying Greenshkined Insect by the United Earth Federation are a species of green-skined humanoids native to the planet called Irk. These beings have a complex history having stages of sanity (Orginal Irken Empire, Irken Hierarchy, Irken Republic) and insanity (the Irken Empire ruled by the control brains).
"well, we have just found out about the Irken skeleton, it's incredibly resilient and heals at a extraordinary rate. How we came to find this is our slow timing to get to the wounded Irken soldiers, namely those with broken bones, when we cam to them, their bones healed, but it healed in a unnatural position, so, we had to break their bones again and set it properly"
- Dr. Richard Chandler's journal
The Irkens are very secretive about their species biology, however, it is known that the Irkens are humaniod insect like species with three fingers and two toes and have a skeletal structure that resilient and heals quickly (a fact that was accidentally discovered by Allied doctors when they were treating wounded Irken soldiers)