That's a difficult question, and it would depend on how you measured "worst," and what actions you think are worse than others. There are a lot of mass murderers, serial rapists, child molesters, creepy scientists that learned things through torture and pain rather than trying to heal, etc. Some people would choose someone who did something offensive in a religious context, etc.
Here are some of the possibilities:
Here are some other possibilities from online lists:
There is no real definitive answer to this as the response will be someones opinion. There are no statistical records highlighting such players.
Muhammad (Peace Be Upon Him)
The fastest person who ever lived is Usain bolt.
Hitler was the worst person to ever walk the earth!
it will vary by the person's opinion
adolph Hitler
absolutely the worst person ever
It is different with each person. The one you hate most is your worst console.
Harry styles worst person is most prob himself ;3(or Maybe taylor Swift)
mohammed
Ellie Ford
Diego Espin and but john Vargas is better