The world was not a mono-culture in pre civilisation times. In some cases in retaliation for killing one of a tribe member they would have attacked and killed every single one of the attacking tribes members. In other cases if a tribe was attacked they would flee and avoid conflict. You can’t generalise the one for one rule to all pre-agriculture societies.
I’m guessing Thug Behram doesn’t count.
As a sub-category, I wonder which woman killed the most in melee combat. Onake Obavva is said to have killed an indeterminate amount of men with a pestle, enough to make a modest pile. The whole story always seemed fantastical to me, though. Khawlah bint al-Azwar seems like the best bet. She took part in several battles and got into the thick of things. She killed five guys when she led a prison escape. Maybe Mai Bhago as an outside chance. Only one battle, but she was the sole survivor.
Not exactly in battle but Mahomet IV’s head executioner, Souflikar, over the course of 5 years strangled to death at least 5,000 people after they each lost a running race to him.
Exactly who I was going to mention. He’s #1 on Cracked’s list of “Real Murderers More Terrifying Than Any Horror Movie”.
“Souflikar didn’t mess around with nooses or axes or any of that bullshit. He strangled his victims to death with his bare goddamned hands.” And according to the article, he wasn’t even an official executioner; his official title was “royal gardener”.
Anyone who’s racking up enough of a body count to be anywhere near in contention is going to have a whole lot of people who want him dead in turn, and the winner is going to have to be someone who survived a heck of a lot of those. Just fighting a lot isn’t enough; you have to actually win a lot. Which suggests to me that the number 1 spot is going to have to go to someone who had a significant technological advantage over his opponents, which probably does mean a conquistador.
A more in-depth article about this race. although Souflikar isn’t explicitly mentioned. It seems like only grand viziers or other notables were given the option of the race.
Also, it seems the “gardener” title included a lot more than just gardening:
Chuck Norris. He doesn’t go hunting, he goes killing.
It’s more about opportunity (i.e. population density) than technology. You could make the argument that the AVERAGE human in pre-civilized times probably killed more people in hand to hand combat than his equivalent in the later times. As there was no concept of an army, any males capable of fighting would have done so when required.
But in later years (in the days of cities and large armies) you had a minority of people who spent their whole lives fighting in huge battles (I am thinking of one of Caesar’s veterans, or a man-at-arms of the 100 years war). Fighting in a single one of those would have meant encountering more enemies than a tribal warrior would have encountered in their entire life (some involved more humans than there were humans on earth in the days when everyone was a hunter gatherer). Obvious most of those people DID NOT live to retire and claim their farm land in the colonies, but some did.
Wait, so there were 5,000 grand viziers and notables who need a good killin’ during this time?
Assuming ‘hand to hand’ could be killing with a bow as well as, perhaps, executing civilians I think some unknown soldier in the Mongol horde who managed to survive from, say the early campaigns in 1206 to, say, 1259 or so would hold the record. You would have major battles fought, towns and cities conquered and in some cases having their populations wiped out by the troops deliberately, and across a mind boggling range of territories. You could be talking about literally thousands killed ‘hand to hand’ in such a circumstance, which is staggering when you think about it.
This thread is about humans.
Also, the problem is going to come from the “best documented” part. People who kill in war usually do not document that fact with any precision, aside from head-hunters …
… though the Japanese in Korea allegedly collected noses for this purpose. Apparently, there is still a shrine of Korean noses collected to document Japanese kills:
The problem, though, was that the Japanese troops tended to pump their numbers up by massacring Korean civilians to add their noses to the “tally”, because they were rewarded per nose. It was a case of nose inflation!
For some reason, this strategy, while it gained Korean noses, failed to win Korean “hearts and minds”. 
Executioners are excluded from competing in the OP, though.
Concerning Roman gladiators: After snooping around for some stats, I’m guessing that even top gladiator body counts weren’t all that high (although, as you say, probably still higher than for your average veteran of several battles, which I actually think says as much about battles as it does about gladiators).
For one thing: The length of a gladiator’s career. At the most, that would be comparable to a modern athlete, or a Roman soldier. So, twenty years, give or take (probably take), at which point they would be either dead or retired (possibly given their freedom at some point, if they were lucky).
For another thing: Gladiators weren’t gladiating (if that’s a word) week in, week out. Apparently, much like modern pro boxers, they would fight two or three matches per year.
For a third thing: The number of fights ending in death for the loser. Not all fights were to the death. (Although I keep hearing that gladiators always fighting to the death is a common misconception. If it is, I have no idea why, since even the stereotypical depiction of gladiator combat has bouts ending with the “thumbs down” or “thumbs up”, indicating that the loser should be either killed or spared. Maybe it’s the idea that such a misconception exists that is the misconception. But anyway.)
These guys were expensive to train, and besides, if they were good, they had fans. They weren’t just killed off willy-nilly. (And when they were killed, I’m guessing that it was by way of “oops, he seems to have snuffed it”, as often as by “thumbs down, finish him off”. That is a guess, though.) The highest fatality rate for losers that I can find mentioned, even when the games were at their bloodiest, is 1/3 or 1/4 of fights ending in death.
So, 20 years times 3 fights, that’s 60 fights, divided by 1/3 kill ratio, is still only 20 dead guys. And that’s *really *pushing it, and assuming nothing but wins.
From the tombstone of one particularly famous gladiator, Flamma (famous in part because he was offered his freedom four times, and each time he chose to carry on as a gladiator, so clearly an interesting sort of chap), as per Wiki:
Once you are talking about battlers of 10s or 100s of thousands of people I don’t think personal vendettas play much role. You do need the luck to be on the winning side and the luck (and skill) not end up on the casualty list, most people did not have enough luck and ended up buried in a mass grave at a battlefield but clearly there were a minority who did and retired after a lifetime of war.
I am now thinking one of Caesar’s veterans who later fought for Augustus would be in the running. Maybe someone like Lucius Vorenus though unlike his TV character counterpart we don’t know what he did after the Gallic Wars.
That said definitely the conquistadors are in the running. The battles they fought in were huge and massively lop sided.
No–I’m pointing that out as a possible discrepancy between the accounts. I’m sure 5000 folk needed killing at the time, but only a small minority of them participated in the death race.
I was also thinking this. Even if bows do not count did the actual killing get done by bows in Mongol armies? I thought the arrow fire broke up the formations more than actually destroying them.
It doesn’t need to be a personal vendetta. An enemy soldier who just has a vague notion that the soldiers of your nation in general need killing, and who ends up opposite you on the front lines, will kill you just as dead as will someone who has it out for you personally. The point is, if you end up in a lot of life-or-death fights, eventually you’re going to get the “or death” option.
Most people, yes, but not everyone. There are plenty of historical examples of soldiers who spent their whole lives fighting in huge battles but survived to retire and die of old age. Yeah, most of the people who fought alongside them were not so lucky, but they exist.
Additionally when it comes to conquistadors they may have been more likely to survive the battles they fought, but not the diseases (which in all pre-modern wars were more likely to kill you than the enemy).
Tropical diseases meant all Europeans (soldiers or civilians) in the new world had a survival rate comparable to most wars.