Alright, it is time for a mod intervention in this thread. If you are coming from outside of our sub, please be sure to read our rules. Speculation is not permitted.

More to the point, do not post in this sub if you do not have a scholarly source to back up your post. Posts that entirely rely on the Church of Satan are not appropriate for this sub, just like sources that entirely rely on any religious organization's point of view. True, you can show how the Church of Satan has understood how and why it uses certain icons, but you need to critically engage the subject matter.

According to The Encyclopedia of Witches and Witchcraft, a small set of the Knights Templar were found to have been worshipping idols referred to as Baphomet. However, the relatively well known modern depiction, was fashioned by Eliphas Levi, a French magician in the 19th century.

Aliester Crowley adopted the moniker Baphomet when he joined the O.T.O. (Ordo Templi Orientis)

The image of Baphomet in an inverted pentagram was officially adopted by the Church of Satan in 1966, in San Francisco. The Hebrew letters spell Leviathan.

A minor contribution, but there are portrayals of goat-headed devils from the early 13th century, in various copies of the Bible Moralisée (Moralized Bible). Here's one example, where a devil is leading away Jews. For more on Bibles Moralisées, check out publications by John Lowden and Sara Lipton (medieval art historians).