Not sure what you're trying to get with here?
Hitler didn't kill people for Atheistic reason
Stalin Didn't either
Neither did Genghis Khan
Or Mao.
Those were all for political reasons.
Mao shouldn't even be on the list near Stalin and Hitler.
People comparing Mao on that same list have, absolutely, no history on China.
Hitler could sensibly be held responsible for tens of millions of deaths in World War Two - including at least seven million non-Jewish Germans. Separately from this he had a program of planned extermination of nine to twelve million helpless prisoners, about half of them Jewish. This was done at the expense of the war effort, a matter of pure rate hatred.
A wild exaggeration of the numbers killed in Land Reform, which was also done by the peasants themselves. And generally was powerful land owners executed for specific crimes: murder or treason, which they had got away with before.
Comparing the NORMAL third-world death-rates that occurred in China during the Three Bad Years (1959-1961) with the greatly reduced death rate that Mao's policies had achieved before that. The worst year had a death rate of 25 per thousand, which in the 1950s to 1960s was normal for poor countries and lower than some.
Famine is the #1 reason as to so many deaths under his reign. With heavy sanctions from the US and USSR, it lead to the death of tens of millions.
He was a far better improvement to China than corrupt dictatorships they had before Mao. This caused a revolution in China. Nationalist party eventually was overthrown, and Mao came in.
Now of course he wasn't a sun-shine guy by any means. But he was the better option for China moving forward instead of the stagnant and corrupt Nationalist Party that ignored the peasants all together.
Anyways, to your question:
We can look to the crusades, which all together, caused the death of millions of individuals (majority innocent).
These include, but not limited to, Pope Urban II, Pope Eugene III, Pope Gregory VIII, Pope Innocent II, Pope Honorius III. For muslims, most notable one is Saladin. (there were also lesser known or not documented leaders also engaging in these wars)
Now with the deaths of millions, we continue onward to the fabulous Inquisitions! (Not even beginning with the Spanish ones!) Their aim by the Catholic Church? To combat "heresy". To name a few, Pope Paul III, Pope Innocent IV, Pope Innocent III, Pope Gregory IX. Coutless of other individuals were also apart of this as well, but less documented. Now onto the Spanish Inquisitions! To name just a few, Pope Sixtus IV, King Ferdinand and Queen Isabella, Ferdinand II, Pope Paul IV, and other lesser names.
To add into the Inquisitions, we have the famous witch trials as well. Hundreds of thousands to near a million of mostly women, died.
Now the list becomes too long when labeling names. I'll just address some big wars throughout the past centuries:
17th century 30 years' war (Catholic vs. Protestant): at least 40% of population decimated, mostly in Germany.
1648 Chmielnitzki massacres: In Poland about 200,000 Jews were slain
Rest of Crusades in less detail: until the fall of Akkon 1291 probably 20 million victims (in the Holy land and Arab/Turkish areas alone).
The list goes on...