The Project Champion is the person who "takes the ball and runs with it" as we say in hockey.
This is usually starts as the person who generates the idea - but then may migrates to someone who believes that this thing really needs to be done and and sets out to done it.
The Project Owner and the Project Champion may be the same person - but often as the project matures the Owner (who probably has money) may pass it back to the Champion to keep the dream alive - while the Project Manager - some hired gun, mercenary type who probably only has a whole lot of experience and cat-herding skills - just knows how to get things done; whether they are excited about them or not.
The Project Champion may not even be a paid position, and they may only participate at flag waving ceremonies - but they must be the person who drives the vision and keeps people enthusiastic.
Are YOU a Project Champion for your own project or somebody else's?