Walter Sherman is a Former U.S. Soldier and Iraq war veteran. Something happened to Walter during his time in Iraq that modified his brain to make him want to never stop trying to find what he is looking for. Because of this, he is afraid that if he gets treatment, his skills will disappear. Though Booth acknowledges that Walter's skills are useful, he holds him in some contempt. During his time in the Army, he went AWOL when Rebecca was about to give birth, and Walter, working for the military police, tracked him down and arrested him moments after Parker had been born.