An open, frank conversation sounds like the best approach. He might be entirely reasonable and helpful to have as a stakeholder in the future. But if you are

An open, frank conversation sounds like the best approach. He might be entirely reasonable and helpful to have as a stakeholder in the future. But if you are at an impass, and you really feel strongly about it, press the 'delete' key and start over from scratch, except this time have vesting over multiple years for the founders stock. This way if anyone bails before the company is up and running, they will get a percentage based on their time invested.