flunky n.

c. 1300, fotman, "soldier who marches and fights on foot," from foot (n.) + man (n.). It also was used in Middle English with a general sense of "an attendant on foot" (late 14c.), and Middle English also had fot-knave "servant of low rank attending a knight or squire" (mid-14c.), fot-folwer "foot-servant" late 14c. fot-mayd (late 15c.) "maidservant, serving woman." 

Later it was used specifically of personal attendants to a person of rank who ran before or alongside his master's carriage, ostensibly to keep it from spilling and otherwise assist it on the road, but also to indicate the importance of the occupant.

The non-jogging "man-in-waiting" sense is attested from c. 1700, though the running footmen still were in service mid-18c. Related: Footmanship.