The Duck is the main character in all three of the Duck Songs. He is yellow, and his catchphrase is "Got any grapes?"
He uses this catchphrase over and over again to likely annoy the people he asks, such as the lemonade stand man.
The mystery is why he asks for grapes, and this is answered in the official duck song book, where it is revealed that he was saved by a boy after nearly drowning. The boy gave him some grapes to eat and they became best friends until the boy went to college. He would often wait for the boy to come back. One day, he saw a man that reminded him of his old friend. So he asked his signature catchphrase,"got any grapes?''