Irgun The Strange serves under Commander Vaako as his best soldier.
His armor is deeply scarred and a possibly decorative knife is stabbed into his back. He keeps it as a trophy of a previous battle and as a symbol of his mastery over pain. He never speaks, simply grunting and growling as he stalks his prey, which either indicates he is unintelligent or he is very reserved and chooses not to speak.
During the invasion on Helion Prime, he finds and kills Abu al-Walid. Riddick follows him into the Great Hall and waits as the Purifier preaches to the crowd. When he refused to submit to the Lord Marshal's offer, he instead demanded to "take a piece" of Irgun. Irgun takes up two large axes while Riddick steps up empty-handed. When Irgun staggers from a high swing, Riddick slips past him and removes the blade from his back. Riddick disengages beneath his defense and stabs him three times, thus killing him.
The Lord Marshall identifies him as one of his best warriors to which Riddick replies "if you say so," clearly unimpressed with him. Then presents the knife to Riddick explaining to him that "you keep what you kill".