In my opinion, the person should be clear why (s)he wants to do a startup. Does the person aspire to (hopefully) earn a lot of money in a relatively short time, or is it sheer satisfaction of doing your own thing or some other valid reason?

It might be better if your core thinking and goals, match to some extent with your probable co-founder.

Having said that, the 'skill set' of the person should compliment yours, so that as a team you are able to achieve more.