[gojomo]

Keep in mind that sometimes people misperceive each others' real contributions, because of differing competencies and priorities. But, assuming your estimation is correct:

Is an employee agreement and vesting schedule in place?

Who reports to whom? You haven't mentioned formal titles/roles, but unless you're already final-say CEO, you'll probably need the board's support to oust him. You'll definitely want their support and advice, especially if adversarial steps to adjust equity or reorganize are necessary.

Talk to older mentors/lawyers who've seen similar situations.

Look up 'shotgun clause'; even if one doesn't already exist, a 'him-or-me' game of chicken might be resolvable with minimal damage/legal-risk using some sort of similar bidding/step-up-or-leave arrangement.