DARPA stands for Defense Advanced Research Projects Agency, and this man though i know little about him as well plays a minor role. Well only because his true self is killed days before snake's arrival. It is later revealed that the DARPA cheif snake first encounters is another member of fox-hound named : Decoy Octopuss. Decoy drains the blood of his victums, in order to copy them in every way. he was placed in the cell, in hopes that snake would spill any information about the PAL key and activating REX. Unfortunately, decoy was killed shortly after communicating with snake, thanks to FOX-DIE.