Dr. Claus Penrose is a former colleague of Walter Bishop. He is introduced when Olivia Dunham goes to question him while investigating "The Brain Surgeon" murders. Walter claims that Dr. Penrose "suffered from severe Pseudofolliculitis nuchae", which Peter specifies as "razor burn". Towards the end of the Vietnam war, Penrose ran experiments on rapid growth and manipulating growth hormones. When asked about it, Penrose states his and Walters work was highly theoretical, but above all "wrong". He resigned from the United States government after working for them for only one year. After his resignation he was harassed by the government and threatened with deportation.