Irken PAK

"An Irken PAK. Irkens like Zim, Zir and Tak always use that for intelligence, weaponry, and everything else. It is essential for Irkens, because an Irken PAK is for the blood of Irkens. A beating heart for them. They're used to give Irkens life also. If they need it, then they will live longer and strong. Without it, they would die after ten minutes, if they don't wear their PAKs soon."

--Su Ji-Hoon, Coming in Peace

An Irken PAK is a backpack-like device that is grafted to the spine of every Irken upon their hatching. Serving as a secondary brain, the PAK contains all of an Irken's personality and statistics. It is never revealed what PAK stands for, or if it stands for anything at all other than a variation on "pack."

Purpose
The device contains all of the Irken's knowledge, effectively serving as a auxiliary brain, and it holds a great array of weapons and tools. It also contains the host's personality, charging cell, atmospheric processor, and a handy auto-reset that will "reactivate" an Irken if they suffer a fatal injury (Plague of Babies). The Irken host's job is encoded into the PAK's programming, and can be changed instantly by a Control Brain (which can also delete all data in the PAK; such is known as deactivation).