The Reapers are the main villains throughout the entire Mass Effect trilogy, but their history begins long before the events of the first game.
In Mass Effect, why do the reapers do what they do (i.e harvest human beings)? What is their primary motivation? - Quora
Mass Effect 3 - Wikipedia
Mass Effect: The Origins & True Nature of the Reapers
Mass Effect: 10 Things You Didn't Know About Leviathans
Reaper, Mass Effect Wiki
Timeline, Mass Effect Wiki
All That Matters is the Ending: Mass Effect 3 – The Writer's Block
Mass Effect 1,2,3 & Andromeda Timeline with relevant events that I think can connect the games : r/masseffect
Mass Effect - Who MADE the Reapers? (Leviathan EXPLAINED)
Mass Effect timeline, explained - Dot Esports