User blog comment:Commdor/Mass Effect 3: Leviathan trailer released/@comment-4118072-20120824201408/@comment-1679409-20120824221113

A theory I've seen says that Leviathan actually won't be a Reaper but is one of the survivors of the race that created the Reapers (and thus became Reapers when the Catalyst took its mission to the extreme).