Bell cow

[he] also keeps a number of cows, one of which has a bell hung round its neck, which keeps ringing with every motion of the cow. The other cows follow the “bell cow,” and thus their whereabouts in the forest are readily got at.

Source: wiktionary

The mornings were rosy, the noontide shone with a deeper red, but the evenings came, serenely stealing, it seemed, out of the heavily-wooded land, spreading over the fields and creeping along the hill-sides where the bell-cow rang her melancholy curfew.

Source: wiktionary

When Carlos Hyde was selected in the second round of the 2014 NFL Draft, it was presumed he would eventually take over Frank Gore's role as lead back for the Niners. Now that Gore signed in Indianapolis, the door is wide open for Hyde to seize that opportunity. "He looks the part as far as a bellcow running back," Bleacher Report NFL analyst Chris Simms said of Hyde.

Source: wiktionary

Goldman is used to taking the lead. In fact, The Wall Street Journal’s Susanne Craig reported that other firms were standing by on a “Lloyd watch,” waiting to see what precedent would be set by Wall Street’s traditional bell-cow. As those firms now make their own inevitable bonus decisions, they will have to settle for “me-too” stories.

Source: wiktionary