Bill is fictional but theoretically a dedicated fan could create him if tulpas exist.

What is Bill cipher based on?

The evil demon, Bill Cipher, is based on the Eye of Providence symbol, but wearing a top hat and a bow tie. Blendin's name (Blendin Blandin) is a pun, because he is hidden in the background. He is "Blendin'" with the crowd. The names of multiple characters make references to things in real life.

Does Bill Cipher lie?

Bill could enter Ford's mind at any time, and with his help, Ford built the portal. However, after Fiddleford came out of the portal traumatized by the horrifying things he saw, which were Bill's actual plans, Ford realized Bill had lied to him.