second fiddle

noun3

1. •
   A fiddle part in harmony to the first fiddle.

   • The second fiddle on that tune is almost as hard as the first fiddle.
2. •
   A sidekick or subordinate, or the role of such a person.

   • I'm tired of being your second fiddle!
3. •
   The person playing second fiddle.

   • I've been second fiddle in that orchestra for ten years now.