Thank you! That shed a lot of light into why he feels entitled to part of the company. This is a risk any technical founder faces if they assign their IP to a company and then agree to a vesting schedule to earn their equity in the business. If that's what happened I don't think he has much legal ground to stand on but I'm sure the lawyers involved will want to argue otherwise, after all I bet they stand to earn 30-50% of whatever is decided as a contingency fee.
Partnerships. They are the ship you launch that you expect to sink.