Behram of the Indian Thuggee cult has been credited with strangling anywhere for 125 to 931 people.
I hate following my own messages with more commentary, but while we’re on the subject of excutioners and war, it’s hard to leave out the Einsatzgruppen. Without creating a debate on numbers (or the holocaust in general), as few as several thousand Einsatzgruppen members were responsible for killing a million Jews in WW2. There is little doubt that some small number of unnamed member of the Einsatzgruppen were on Zyklon B duty at Auschwitz, and as “executioners” (pardon the weak term), killed many, MANY more people.
If we’re counting war duty, while this answer is probably out of the scope of the OP’s question, there is no doubt that Paul Tibbets holds this dubious record.
From the OP:
Sure it’s kind of a weird line to draw but it’s the OP’s thread. He is looking for something more personal.
Aside from being explicitly outside of the scope of the OP, there’s the detail here that the person who actually released Little Boy - and who was physically in control of the plane as he did so - was not Tibbets, but the bombardier Thomas W. Ferebee.