The Knight Bus is a vivid purple, triple-decker bus that provides emergency transport for the stranded witch or wizard. The name “The Knight Bus” is written in gold lettering across its windscreen. Its interior changes depending on the time of day. By night, the bus has no seats; instead, half a dozen brass bedsteads are arranged along the windows. By day, the bedsteads are replaced by a collection of mismatched armchairs. A large chandelier hangs from the ceiling of the first deck, and a narrow wooden staircase provides access to the upper levels. The ride is notoriously bumpy and violent, with the bus's contents, including beds and passengers, sliding around as it lurches and screeches to a halt.
The primary function of the Knight Bus is to provide rapid transport for any witch or wizard in need.
The concept of the Knight Bus was first proposed in 1865 by the then-Minister for Magic, Dugald McPhail. The idea was inspired by the newly popular Muggle bus services and was designed to provide a discreet method of transport for underage or infirm wizards who could not Apparate. The proposal was initially met with resistance from pure-bloods who objected to adopting a Muggle invention, but it was eventually approved and has been in service ever since (Pottermore).
The Knight Bus serves as a crucial mode of transportation and a source of information at key moments in the series.