Lead Rider of [[Kamen Rider W]], twentieth show of the Kamen Rider series and eleventh of the Heisei generation.

Self-proclaimed "hard-boiled" private eye [[Hidari Shoutarou]] and his enigmatic assistant [[philip_(kamen_rider)|Philip]] combat Dopants, humans turned into monsters via [[Gaia Memory|Gaia Memories]] to wreak havoc in the city of Fuuto, using their "true" Gaia Memories and the Double Driver to merge into Double.

Double has two halves split down the middle, with Shotaro forming the body and left half, and Philip the mind and right half. Each half has 3 forms, making for 9 combinations, of which the most prominent is CycloneJoker. Other forms include FangJoker (where Philip becomes the body and Shotaro being the mind) and CycloneJoker Xtreme (with both men merged as one).