The Pentagon Thief is a special round enemy from Call of Duty: Black Ops. He is featured in the zombies level "Five". He does not hurt you, but he does steal whatever weapon you currently have drawn. He only arrives once the power is turned on.
My theory about the Pentagon Thief is that he was the creator of the Winter's Howl. He had only made one and the US government wanted more. But he refused once he saw the stolen Thundergun. (In "Five", you can see a Thundergun near the AK-74u. It is unusable.) He wanted badly to repair the Thundergun, which had been damaged upon arrival. The government knew that he could repair it, so they allowed him to take a break from the second Winter's Howl.
But when he researched on how to fix it, he only found a list of endless numbers. He went insane trying to remember all the numbers. He knew that, if he could memorize them all, then he would be able to complete the Thundergun.
But, while fooling around with the Winter's Howl, he accidentally froze himself. He was put in the morgue and was dead even after he thawed. Since then, scientists had begun studying the Winter's Howl in order to replicate it. But the zombies broke out and all of the scientists went missing (either were turned zombie or went into hiding so they wouldn't die).
But the Pentagon Thief was not unaffected. He was brought back to life. Seen behind him are the numbers that made him go insane. But the ice had done something to him. He wasn't craving brains; he was craving revenge. The government had taken away his Winter's Howl and now he wanted it back. He takes the players' guns in hope to get his own weapon back. But even when he does successfully steal the Winter's Howl, he won't stop until you're dead.