"You are the man behind the curtain."
Translation:Sei tu l'uomo dietro la tenda.
In Italian the subject CAN be implied, and put in many different positions. I will show you the different nuances in this case.
Sei tu l'uomo dietro la tenda. = L'uomo dietro la tenda sei tu. = I have tried to understand it, and I am sure it's you the man behind the curtain
Tu sei l'uomo dietro la tenda = You are the man behind the curtain, maybe there is somebody else you were speaking about and you want to stress the contrast of who is who and where they are.
Sei l'uomo dietro la tenda = no particular nuance.
To be short and sweet about it ceceg, tu is not needed at all. all tu does is make it even clearer that it talking about you. The sentence could translate to tu sei, sei tu, or just sei.