The Free Jaffa, formerly the Rebel Jaffa, are an offshoot of humanity genetically engineered by the Goa'uld System Lords to serve as slaves and soldiers. Of all the modifications to their physiology, their unique abdominal pouch is most-prominent, and serves to incubate larval Goa'uld for later implantation. The infant parasite provides increased strength, longevity, and health, at the cost of supplanting the Jaffa's natural immune system, effectively forcing them on lifelong dependence until the development of tretonin.