The role of the individual doesn't matter as much as a) their level of contribution (typically in time and/or skill) and b) how critical they are to succeed.
If you only had the idea and couldn't launch the business without them, then they are an equal partner. If you had already built the product and were looking for them to join you to take it to market, then perhaps it's a smaller share.
Unfortunately there's no set rule for this - it's really up to you and your partner to determine what you feel comfortable with.
A couple of ideas worth considering, though:
1) If you're asking because you're worried about them walking away from the deal and taking shares with them, you could consider setting things up such that they would gain increasing ownership over time.
2) If you're worried about being equitable, then something that's worked well for startups I've participated in, is to determine how much our time is worth, then track time, and issue shares to ourselves in lieu of money. So, if your time is worth $100/hr and you put in 2000 hours in the coming year, you may issue yourself $100 x 2000 = 200,000 shares. Likewise, if you determine that your partner's time is woth $150/hr (maybe they're more experienced?) and they only put in 1000 hours, then they would get 150,000 shares. Everytime we've done a variation on this approach, everyone has felt that it was very fair.
Hope that helps!