dispatch rider 
noun British
A messenger who delivers urgent business documents or military dispatches by motorcycle or (formerly) on horseback.Titchmarsh carried out his duties as a dispatch rider first on horseback and then on a motorcycle....
- Anybody who wants to be a cycle despatch rider will tend to be a little alternative in their thinking, Mick admits - so it seemed natural to turn to a complementary health centre to keep them in shape.
- A dispatch rider at the start of the First World War, Portal was soon commissioned and then seconded to the Royal Flying Corps in which he served with distinction.