flag carrier

noun5

1. •
   A person carrying a standard or flag, usually at sporting events and parades, previously on the battlefield.
2. •
   A transportation company, such as a shipping or airline company, that is registered in a given state.
3. •
   A national airline (typically having the flag, or other national insignia, on the tail).

   • I'll be interested to see how this service does. It will be basic with fares to match, so will be akin to a budget airline taking on a flag-carrier. — 2021
4. •
   A strong supporter of a cause, or perhaps the strongest and most visible supporter of said cause.

   • Bill was the flag carrier of the movement to improve inner city education.
5. •
   An aircraft carrier serving as a flagship.