Bill Cipher (I'm not the person who made this I just edited it)EditBill Cipher is an actual character in a television show called "Gravity Falls" in Disney Channel.
Bill is NOT a Triangulum. This is a common misconception, and is most often mistaken for a Triangulum due to his current running relationship (engagement) with TG, via Trichat.
His age is currently unknown, though speculated to either be frozen due to lack of time (putting him at somewhere between an estimated 22 - 24 years in reality, even though trillions of years have passed) or intangible.
Bill's first appearance is in season 1 episode 19 "Dreamscaperers" in this scenario, Gideon Gleeful is trying to steal the deed to the Mystery Shack in order to set up "Gideon Land" so he ends up summoning Bill Cipher to do his dirty work. Bill goes into Grunkle Stan`s mind and is trying to find the passcode before Dipper, Mabel, and Soos finds it.
Stanford (The Author) and Stanley (Grunkle Stan) switch clothes and makes Bill beleive that Stanley is Stanford. Bill ends up being trapped in Stanley`s mind and is erased by a memory erasing gun.
This, however, varies from dimension to dimension.