I think you are more likely to get a good answer or discussion from asking this in /r/AskScience.

There are plenty of animals known to have killed humans and fed on them. Do you mean an animal that only ate humans?

Examples of occasional maneaters include:

• Big cats (tigers, lions, leopards)
• Cougars (not big cats despite their size)
• Hyenas (though it's difficult to tell if they killed humans or only fed in corpses)
• Canids (wolves, coyotes, wild dogs)
• Brown bears
• Crocodiles and relatives
• Sharks

In addition, there is some fossil evidence of early hominid predation by birds of prey and (more dubiously) sabertooth cats. Feel free to ask for more detailed examples.