I've been researching this a lot lately. So this could be from other posts on HN, other forums, or blog posts... most of this is probably not my original though

I've been researching this a lot lately. So this could be from other posts on HN, other forums, or blog posts... most of this is probably not my original thoughts. First the right co-founder would be a lot like you. Compatible communication styles and temperament. If one of you likes to "call it like it is" and the other is more gentle, things won't go well. You don't have to be identical, but close enough to not waste time fixing your relationship every day. Second, the right co-founder will be the opposite of you. In terms of skills, opposites are good. You're good at development? You need them to be great at something entirely different. If you met your best friend because you worked side-by-side doing the same job and do everything together, probably not a good cofounder. But if you have a former colleague that you worked with, you got along great, but you were in sales and he was a developer -- that might be a match made in heaven. I like to think of it like a marriage. My wife doesn't mind doing the things I hate (cook, clean, etc) and I love doing the things she hates doing (going to work, doing finances, etc). We communicate well, get along great, and the responsibilities are easy to split.