outrider

noun

1. A guide or escort, especially one who rides in advance.

   “Then they went from farmhouse to farmhouse, two little girls walking at the head of the procession as bridesmaids, and six or eight outriders galloping ahead on hobby-horses to announce their coming.”

2. One who rides out on horseback to inspect a ranch etc.
3. (figuratively)A forerunner.

   “The Winchester MP is something of an outrider for a new project now: moving his party into the space vacated by the Conservative shift to the right under Iain Duncan Smith.”