When Richard Wagner was scoring Das Rheingold in 1853, he originally envisioned a quartet of trombones. But trombones lacked the haunting tone of French horns, and so Wagner commissioned four instruments he called Tuben or "Tubas."   While it is called a "tuba," French horn players rather than tubists typically play Wagner tubas. The fingerings and mouthpiece on a Wagner tuba are identical to a French horn, and like French horns, the Wagner tuba comes in B♭(tenor) and F (bass) keys.