What makes someone an awesome co-founder CTO?
Is there criteria that I should look for?
Number one, they must share your vision. Number two, they should be smarter than you. Number three, they should over-communicate.
Number one implies that you're clear on your vision in a way that you could recite those two sentences about the ideal experience of your company for any customer (external or internal) by heart.
Those are the easy answers. But I also encourage you to think about how you would run your company without a co-founder. Don't focus on titles. Focus on requirements. Know that you will need other people to support you. A co-founder is only someone who 100% shares your vision. It is not a first or early employee. A head of technology does not have to be a CTO. A CTO is something very specific.
For every founder you add, including the first, decisions become harder exponentially. While this is CoFoundersLab, you may find that you simply need support, not another founder.