standard-bearer 
noun
1A soldier who is responsible for carrying the distinctive flag of a unit, regiment, or army.Caesar records the standard-bearer of X Legion in the Roman invasion of Britain who, seeing his comrades reluctant to disembark, jumped into the surf and obliged them to follow him or lose their standard....
- The standard-bearer and the battalion commander are a scant ten up from me, leading the march.
- As a Volunteer he was his Unit's standard-bearer and fought in the 1916 Rising.
1.1A leading figure in a cause or movement: the announcement made her a standard-bearer for gay rights...
- When Ali refused the draft, there was no genuinely mass anti-war movement in the country; not long after, he would become one of the standard-bearers of that movement.
- The original standard-bearers of the U.S. gay rights movement get their due in a new documentary
- He is, warts and all, our standard-bearer and founder of our Republic.