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, and 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.
The Prince of Lies is another example of a vampire so ancient that its human features are little more than a shadow to the monstrosity it has become. Other such vampires include The Master and Kakistos.