"Ride of the Valkyries" is a classical music piece developed by Richard Wagner during the late 19th Century, which played during the beginning of Act III of his second opera, Die Walküre.
It was frequently utilized by Hitler during World War II. It's most famous use in popular culture was in the gunship scene from Apocalypse Now, which led to it being played when gunship rescues or last-minute cavalry arrivals for the heroes occur in popular culture. Ironically, the music was intended by the producers in that instance to imply the gunship crews were villains.
The piece was utilized in the demo for Metal Gear Solid V: Ground Zeroes, then titled simply as Metal Gear Solid: Ground Zeroes, as pre-selected music for Big Boss' gunship to play when extracting him from Camp Omega, although the creators confirmed that other music besides "Ride of the Valkyries" could be chosen by the player to play. It was included in the final version of Ground Zeroes, both as a standard Walkman track, and as selectable music for the gunship's landing.