be second fiddle (to someone)

To have a role, position, or part that is less important than or subordinate to that of someone else. I'm really sick of being second fiddle to this ignoramus—I'm the one who deserves to be the star of the show! He had aspirations of moving ahead in the company, but it seems like he's destined to be second fiddle for the foreseeable future. Tom often felt like he was second fiddle to his older sister because of all her achievements in sports and academics.