second banana

Noun

 * 1)  A comedian who plays a secondary or supporting role, especially as straight man and traditionally in vaudeville or burlesque theatre.
 * He grew disenchanted with playing second banana and never getting credit for the laughter.
 * 1)  A person who serves in a supporting, secondary, or subsidiary capacity; an assistant.
 * The plumber left his second banana behind, to finish installing my new sink.