I think my vote would have to be Tesla’s processes enabling the effective creation and transmission of alternating current.
And I have to strongly disagree with agriculture as a most important invention, assuming we’re talking about “important” in a positive sense.
Agriculture introduced incredibly straining labor, transferred humans from, for the most part, independent hunter/gathers into co-dependent collectives, shortened lifespans due to the inherently unsanitary conditions of communal living and gave us the dual evils of institutionalized religion and government that we’ve spent 5,000+ years and still haven’t shaken off, despite our progress in almost all other areas.
That being said, I’m still not planning to move to the woods anytime soon, don’t get me wrong