In the famous movie, Dorothy is in the magical land of Oz and wants to get back to Kansas. She approaches what she thinks is the Wizard, a giant projected image with an amplified voice. Her little dog Toto accidentally pulls down a curtain and we all see that the wizard is an ordinary man with a microphone and a projection device. In a very famous line, the man has the projected "Wizard" says, loudly: "Pay no attention to the man behind the curtain!" The phrase has become a saying or image for the relationship between a false, larger-than-life, powerful image and the weak "man behind the curtain" pretending to be something he is not.

As Phil states, it's a film reference. In "The Wizard of Oz" the wizard is just an ordinary man who hides behind lights and sound and special effects to make himself appear far more powerful and impressive than he really is. He wants to appear important and command attention and respect, but he really doesn't have the special abilities that he pretends to have. I think there's a word missing from your sentence, since it seems to be discussing a narcissistic person. A narcissist is obsessed with himself and how he appears to others, so the writer is comparing a narcissist to the Wizard of Oz. Here's the scene where he's revealed as a fraud: https://www.youtube.com/watch? v=YWyCCJ6B2WE

It's a reference to a classic American movie: https://www.wikipedia.org/wiki/The_Wizard_of_Oz_(1939_film)

In this context, a 'front' is similar to a 'mask' or using a different persona. Because Oz is 'flawed and human'' in reality, he wishes to hide these traits by putting on a 'front'. This gives the illusion that he is anything but 'flawed and human'.