Definition from Wiktionary, the free dictionary
wheelhorse (plural wheelhorses)
- A person who labors heavily for a particular cause, without being concerned about recognition
1997, David Backes, A Wilderness Within: The Life of Sigurd F. Olson, ISBN 0816628424, page 369:
- He was a wheelhorse, a tower of strength, to the Park Service and to the forces that were trying to establish new parks, seashores, canoe wildernesses, and other reservations during the Kennedy and Johnson years.