Not in a great man theory sort of way, but who would you say is the worst living human today? Sometimes I get too bogged down with thinking about our issues as systematic and forget that all policy has someone signing off on it and that got me thinking and I've arrived at Bill Gates. With his work in Africa, how he ruined computers for the world, and the Epstein ties I'd say he's gotta at least be up there.
I'm gonna go with a less intuitive one: Carter, depending on what you consider "direct." Between greenlighting a lot of atrocities from US client states, sending weapons to warlords in Afghanistan and to the genocidal Indonesian dictatorship, and helping to mainstream neoliberalism, his actions have without question left a long and bloody wake.