As a venture capatalist I believe the key people in any start up should be incentived with equity. As someone mentioned below the equity in itself has no value as 100% of nothing is nothing. If he is good enough he will add more value to you and your partner than the equity you provide. Also if the equity is sufficient, which you should cliff vest over at least a 4 year period, he will be fully incentivized to stay and help build a sustainable profitable asset of value.