You'll soon learn that a great business has far less to do with the idea, and far more to do with execution. There are probably a dozen other very smart people working on the same thing right now, if it's truly a great idea, so the question isn't whether you can build it better than this other fellow, but whether you can execute better than all the others out there that you don't know about.
If you think he deserves a piece because it's that revolutionary, then cut him in and tell him what your concerns are with his participation. Any great partnership is based on clear lines and responsibilities being drawn. If he refuses to compromise to work with your team, (or vise versa), then you'll have tried, and your conscience will be clear to proceed, and he'll have had the opportunity to walk away.
If you think he deserves a piece because it's that revolutionary, then cut him in and tell him what your concerns are with his participation. Any great partnership is based on clear lines and responsibilities being drawn. If he refuses to compromise to work with your team, (or vise versa), then you'll have tried, and your conscience will be clear to proceed, and he'll have had the opportunity to walk away.
The other poster was right. Just build something.