There must have been at least 2000 priests involved in that, though, assuming 10 seconds per sacrifice and 12-hour work shifts. That comes out to an average of 500 per person, which I guess might be a record if you don't count wars or acts of terrorism, but that cuts out an awful lot of people.
While it was done during a war, and sanction by his government, the act of killing the most people by one person directly would have to be the bombardier who release the atomic bomb over Hiroshima. Estimates are 80-140,000 people were killed. A lesser amount at Nagasaki, though still close to 80,000, would make that bombardier #2.
Indirectly, of course, Stalin probably wins (30M+), unless you wish to lay the blame for nearly all deaths happening in Europe during WWII as Hilter's.
Torturing the numbers. Hear them scream.