I think it would be vital to the company's survival that roles and responsibilities are clearly defined. If there's grey area, I've found that work tends to gravitate toward the more motivated party, and the social/power structure gets weird.

I started a company with four founders, and we didn't define roles. What ended up happening is one person didn't do anything that wasn't interesting to them, one person would start a bunch of tasks and leave them half-finished for someone else to handle, and one person was only capable of handling process-based work, which left the fourth person (me) to handle everything else (and write the processes).

It bred resentment and made it very difficult to adjust roles going forward, because it had been established that I could do everything and therefore I became the final point of responsibility, even if we'd defined new roles later. Our only way out was to sell the company.

In later companies, I laid out responsibilities clearly and made sure each founder had ultimate responsibility and autonomy around their tasks. This has worked out FAR better in every case.

I've built a framework that I use for defining and divvying up tasks, and it's made a huge difference. I've had my coaching clients use it as well to similar results.

If you need a fresh set of eyes on it, or if you'd like to bounce ideas, I'd be happy to talk. Drop me a request and we'll talk.

Good luck!

"Other Jason" gave a great answer.

Define the roles and responsibilities, and keep communication open and frequent. If you don't you'll end up in the lopsided work situation.

When I've let other people (and myself) do what they want, when they want, productivity suffers. And when you're in the race to profitability, productivity is what you need.

I started my first tech startup with a friend where he had the initial idea and then I joined him to develop the same further. So I understand what you are referring to.
Since you have a team of 4 - I am wondering why are you only talking about the the other co-founder. I assume here the roles & responsibilities of the 2 techies are clear to all 4 involved.
Its always a good idea to have a clearly defined set of tasks between 2 co-founders. To define the same you need to look at what needs to get done and who is best suited to do it. Some areas like product demos/ reaching out to contacts etc can be shared. However the core responsibilities should be clear in terms of what you & the other person will "get done"
This is necessarily a collaborative & exploratory process between the 2 of you or 4 of you. If you encounter trouble on this path - its best taken head on & addressed as those issues could or rather will come back to bite you hard.
I hope this helps. In case you need any further specific intervention please do let me know. All the best.