El que da las órdenes, el mandamás
A backseat driver is a bossy person who tells others what to do. Someone who gives unwanted advice or instructions.
Many rich people ride their cars in the backseat and tell their drivers where to go and how to do it. They can even change their minds on their way and ask the chauffer to stop or whatever they may feel like. We become backseat drivers when we take a taxi. But expand this meaning to mean that somebody is giving unwanted, annoying orders, suggestions or instructions that no one else has asked him to.
I hate my mother-in-law. When she comes visiting, she starts telling me and my wife how to educate our children, take care of them, feed them and even how to dress them. I try not to be rude and I keep myself quiet but it is so unpleasant to have such a backseat driver in my house all day long.