This is good advice, but you need to be sure that the person is "co-founder" material. I have personally been involved in startups where someone who was a top-notch coder, but a horrible "businessman" was given co-founder influence on the company (they never had an official co-founder title, but effectively had the same ability to impact the company and make decisions on things).

Some people are brilliant at implementing a concept, but utterly horrible at pretty much every other aspect of running or building a company.

Just because this person would be instrumental in getting the working code going does not mean that they are at all qualified to shape the business...