The Prince of Lies was an ancient vampire who was captured by the Third Reich during World War II as part of an effort to surgically alter vampires on a psychological level in order to create an army of vampire-soldiers.
In 1943, he was trapped in a U-Boat alongside Spike and Nostroyev. Together, they killed most of the boat's soldiers until Angel arrived after being kidnapped as well to prevent them from causing any more damage. Upon learning of the purpose of his capture, an enraged Prince of Lies attempted to kill the only German left on the sub. He was stopped by Angel with a stake through the heart. Before he died, the Prince threatened to suck out a Nazi's brain and digest his thoughts. It is unknown if this is a description of some unique ability of his or just a creative threat.
Much like the Master, the Prince of Lies is inspired by Count Orlok. Also, like the Master and Kakistos, he is one of the few Buffyverse vampires so ancient that he is able to out live any of his human features.