User blog comment:Legionwrex/What do Reapers do in their spare time?/@comment-2127131-20120731185742/@comment-1679409-20120731194818

LOL!

Reapers 1 and 2: Wait! The Protheans advanced them! They cheated! We're not paying you anything.

Reaper 3, known to his friends and family as Leviathan, then precedes to slay Reapers 1 and 2. So, now we know why Leviathan killed another Reaper: they wouldn't pay their debts.