Startups require a flexible, creative, open-minded team. A company that succeeds without pivoting multiple times is the exception that proves the rule. A co-founder has to believe in the vision enough to be able to sacrifice EVERYTHING for the sake of achieving success. Your co-founder must realize this job is more than a paycheck.
The essential qualities that you should look for in a co-founder are:
The founder should look for complementary skill sets in his co-founder. Having different skill sets helps you more easily define your respective roles in the business, and it's invaluable for each person to bring expertise to the table. Also, defining your roles early on makes it easier to hold each other accountable, because the expectations are clearly established. While your co-founder's background should be distinct, the person should have a like-minded attitude and passion to fit the culture of your company.
Your cofounder should be well versed in the actual sector you’re going in to.
Value what your partner brings to the table
You should choose someone whom you think is equally as intelligent and hard-working as you.
If you build it they will not come
A lack of customer acquisition methods and points of distribution is the single largest killer of startups out there. Getting a product to market is certainly difficult, but acquiring customers is even more difficult. Your business cofounder should have a clear vision for how to acquire customers.
Alignment of Mission and Passion
It's obviously important for both co-founders to be invested in the company, but making sure your goals are aligned is essential. Uniting over a common interest is a typical way for two co-founders to be brought together, but you should also ensure that you both are on the same page regarding the future of the company.