Flag carrier

Flag carrier has two common meanings:

• A state-run, state-owned or state-designated transport company or organization, specifically (though not universally required) showing the state flag apparent for public view (state in this context used to mean any principality or country). Example: "Air Canada is its namesake's flag carrier"
• A strong supporter of a cause, or perhaps the strongest and most visible supporter of said cause. Example: "Bill was the flag carrier of the movement to improve inner city education."