Before you go to the board (you ethically should) let ascertain a few things.
Are you sure he's an overrate person or is it just that you don't see the value in his input?
Some where in the thread you mentioned:
> It's going to get real messy, especially since he holds all money, bank, passwords info
Some credit needs to go to an individual who has taken ownership for responsibility of finances, considering the amount of onus that falls on the need to maintain finances optimally for a start-up, this can also be really stressful. If he has mismanaged finances, that's another story.
If he has not mismanaged the finances and has taken ownership/charge of these affairs you need to reflect on why you did not opt to share the burden.
Some people don't like managing finances, nothing wrong with that, but they do need people who'd do it for them, even better if there is a mutual need to succeed. Anyone can be the best money manager in hindsight.
> the 3 employees we have today respect him a lot especially since he's an expert
Respect is very important. Sure, the article says that the Overrated person can establish themselves as an expert, but believing this without a doubt also means that you don't trust the judgement of your first three employees.
Not saying you're wrong, but there is a possibility that you need to delve a little deeper on why they think your co-founder is an "expert".
> following those rules in the article
Not all rules apply all the time. Also these are not really rules but situational observations.
> The only problem I see here is that he has more rapport with them (the board).
Was he instrumental in helping you raise funds? Could you have raised the funds with a 100% surety without him if you were a single founder? Would this rapport help keep the faith of the stakeholders in the prospect of your success?
Maintaining and managing peoples belief in an idea or the people executing an idea is no easy task. Are you sure he has a zero percent contribution in any of these? And again are you sure you could have achieved a 100% of past results without him?
> He actually threatens the company's success if I ever try to "sneak a move" on him
Why would you try to sneak a move past anyone who has as much to loose as you, or even if it was a fraction thereof?
How does he threaten the company?
Does he threaten to leave? If you want him to leave, this solves your problem. But, if his leaving threatens the company, you should probably reconsider firing him.