Citations:bell cow

Noun: "a leader; influencer"

 * 1929,, The Stray Lamb, Chapter 17,
 * She’s her own woman, major, first, last and all time. If she can’t be the bell cow she’s not going to trail along. That’s all there is to it.
 * 1951, Ernie Harwell, “Wanted: A Mr. Baseball,” The Magazine, Volume 50, No. 4, April 1951, p. 23,
 * Who’s the logical successor? Any list would have to be headed by Joe DiMaggio, Ruth’s successor as the bell-cow of great New York Yankee teams.