Assume you achieve total world domination and they make a movie about you. Visualize the narrative arc. Would you think "This guy deserves to be the hero or co-hero of this movie?" If not, you don't want them to be a cofounder.

There are fairly few movies where someone bestows money, a name or an idea on the interesting characters and ends up being really important to the plot.

You want Aragorn, not Elrond, as your cofounder. (Naturally I think of geeks as hobbits.)

P.S. Your co-founder should say the same about you. If you're a tool rather than a partner, fleeeeeeeee.