have a vested interest (in something)
To have a personal stake in something, typically because one could potentially benefit from it. Of course I have a vested interest in how the board reacts to this proposal—if they like it, they might promote me!
have a vested ˈinterest (in something)
have a personal reason for wanting something to happen, especially because you get some advantage from it: He has a vested interest in Mona leaving the firm (= perhaps because he may get her job).