Are the Enderman human?

Notch did prove that indeed the Endermen came from The Farlands and were originally going to be named “Farlanders”. Even though the Farlands no longer exist, exactly how did the Farlands create these twisted mostrositys? They’re human inside.

What is the Endermen backstory?

The Endermen encountered in the modern day are the slaves of the Ender Dragon, they have lost their free will and sanity. Sometimes their builder instincts still show as they attempt to take blocks and stack them, but it is believed that they are too far gone to be saved.