Second Banana Meaning

(idiomatic) A person who serves in a supporting, secondary, or subsidiary capacity; an assistant.

Example:   He grew disenchanted with playing second banana and never getting credit for the laughter.
  The plumber left his second banana behind, to finish installing my new sink.
2012, Michael Smyth, "The lifeboat is filling up", The Province, 30 August 2012:
  When you want to be the boss, but you can't, it's not a lot of fun to be second banana.