this is how the DLC explains the Reapers and the star child
jacked from Neo GAF. i actually like that explanation too bad i can never bring myself to play this game ever again to experience it for myself so i just read it.
the Leviathans were the first dominant species in the galaxy. Every other species was subservient, worshipping the Leviathans as essentially gods. As these species evolved, they eventually created machines that would wipe them out. The Leviathans got tired of trying to micromanage dumb species constantly wiping themselves out, and instead developed a babysitter AI (the Catalyst) to watch over the numerous species of the galaxy. The AI's goal was simple to ensure organic life was preserved.
The AI experimented with solutions to this 'problem', such as guiding organic species along a 'safe' controlled technological path (relays, and so on), but for whatever reason deemed preservation of organic material through 'harvesting' into great singular creatures was the best solution under given circumstances. The first species 'harvested' were the Leviathans, and thus was created Harbinger, the first of the Reapers.
Ever since the original harvest the Catalyst has been using the galaxy as an experimental test bed to find a better solution to the 'problem' of organic preservation, using Harbinger to lead the charge and harvest sentient species in the galaxy for reasons. This is why the cycle is stuck in a continuous loop: as part of it's original programming, the Catalyst is looking for a 'solution' as organic preservation, and it calculates harvests/Reapers is the best it has.
The AI experimented with solutions to this 'problem', such as guiding organic species along a 'safe' controlled technological path (relays, and so on), but for whatever reason deemed preservation of organic material through 'harvesting' into great singular creatures was the best solution under given circumstances. The first species 'harvested' were the Leviathans, and thus was created Harbinger, the first of the Reapers.
Ever since the original harvest the Catalyst has been using the galaxy as an experimental test bed to find a better solution to the 'problem' of organic preservation, using Harbinger to lead the charge and harvest sentient species in the galaxy for reasons. This is why the cycle is stuck in a continuous loop: as part of it's original programming, the Catalyst is looking for a 'solution' as organic preservation, and it calculates harvests/Reapers is the best it has.

