Greek saga - Who exactly is summoning the monsters towards Kratos?

this might be a stupid question because im pretty sure it was explained in a rando line in GoW1 but i dont remember it.

they appear to rise out of Hades and return when they die, so originally i thought it was the man himself just being a dick towards a random spartan for no particular reason, but the monsters keep coming after hes killed. I presume its possible that Zeus or another Olympian takes over the summoning duties but thats never stated, nor is the hades thing as far as i remember.