second banana
US /ˈsek.ənd bəˈnæn.ə/
UK /ˈsek.ənd bəˈnæn.ə/
1.
a person in a subordinate position; a sidekick or assistant
:
•
He's always been the second banana in the team, never the leader.
•
She's tired of being the second banana and wants to take on more responsibility.