Frank Jaeger was born in the 1970's, his parents unknown. He was found in Vietnam by Big Boss, and raised as a war orphan. Big Boss spent years training Jaeger into a supremely destructive killing machine, fully fluent in languages and colloqualisms. He became a mercenary in his teens and experienced various wars. One of these was the Rhodesia Independence War, during which he discovered an orphan baby by the Zambezi River; he named her Naomi and took her to safety. Jaeger was then captured and became a POW in Mozambique. Extreme and bloody torture followed. Jaeger's ears and nose were cut off, and his face was badly scarred. It was only the intervention by Big Boss' mercenaries that saved him.
He then moved to the U.S. with his adopted sister and joined Fox-Hound, achieving U.S. citizenship. Working closely with Big Boss througout the 1990's, his valor earned him the highest commendation possible, the name Gray Fox. This title was proven beyond doubt during the Outer Heaven crisis in the mid 1990s, when he conducted a solo infiltration and succeeded in obtaining classified Metal Gear information. After Big Boss was discharged from Fox-Hound, Jaeger disappeared in similar circumstances, but resurfaced in Zanzibar. He was defeated by Solid Snake, and was thought to have perished.
Jaeger survived the Uprising of Zanzibar, but lost a third of his body. He was saved by being immediately transplanted into a strengthened exoskeleton (called an actuator) under development by the military. He was used as an experimental subject for the gene therapy testing prior to teh Genome soldiers. For the continuation of such experiments, he was drugged, his conscience coming back only 10 percent of the time. Otherwise, he was unable to remember his actiosn until the drugs wore off, after which Jaeger writhed in agony until sedated. His strong will to fight Snake was the driving force that kept him alive .
Recent reports have linked Jaeger to a mysterious Ninja. Clad in optic camouflage, the Ninja executed a Medical Officer of Fox-Hound prior to this mission. The Ninja's actuator suit utilizes a supersonic motor that operates with high frequency voltage. When the wearer changes position, minute electric currents in the muscle are detected and utilized to control the actuating section, giving better than human agility. Not an official member of Fox-Hound, the Ninja may be working with them. Jaeger also used a famous pseudonym in previous Codec calls.