When you hire a celebrity programmer like that, what exactly do they end up doing? Do they actually have responsibilities in their role or is it more just to s

When you hire a celebrity programmer like that, what exactly do they end up doing? Do they actually have responsibilities in their role or is it more just to slap the branding on to them while they continue to do their own thing, whatever it may be? (in Matz case I would think he has more than enough full time work on Ruby itself)