Nico di Angelo is a fictional character in Rick Riordan's Percy Jackson and the Olympians series.Nico di Angelo is Bianca's younger brother, the only known son of Hades. At first Percy assumed Hades broke his agreement with Zeus and Poseidon to not father any more children after World War II, but Nico and Bianca were born before the pact was made, and had been placed in the Lotus Hotel and Casino in Las Vegas, Nevada, a casino that prevents its occupants from aging. This part of Nico and Bianca's background is first hinted at during The Titan's Curse when the gang is forced to enter the Washington Metro to escape a pursuing helicopter. Nico and Bianca both seem to think that the Metro is very new, as it wasn't there "the last time" they went through Washington D.C. - a statement that at first seems ususual, given that they are described as being in their teens, and the first segments of the Washington Metro opened in 1976, well before they would have been born.