In the movie Hereditary the demon Paimon or Peymon / Paymon is invoked
The Real History of the Demon Paimon
The demon Paimon first makes an appearance the ancient text, the Lesser Key of Solomon, than in Johann Weyer’s Pseudomonarchia Daemonum, Collin de Plancy’s Dictionnaire Infernal and finally Book of Abramelin..
In these ancient texts the Paimon Demon is often referred as the king of the west and is also said to be one of the eight kings of hell, with 200 legions of spirits, some of which are angels, and demons; as portrayed in the movie Hereditary. One of the other things that the movie portrays is that it is said in the texts that a sacrifice must be made to summon to summon the demon, was the sacrifice in the movie his sister?
What is the Symbol in Hereditary?
The symbol in the movie Hereditary, is the sigil of Paimon and is used in rituals to summon the demon.

Some modern day Occultists such as Carroll Runyon suggest that the Paimon is ultimately derived from a “a Middle Eastern Pagan Goddess”. This is due to the fact that some manuscripts depict the Paimon demon as a young woman riding a camel, and that the name “Paimon” purportedly meant “a tinkling sound” in an unspecified language, in turn a claimed reference to Isis. The Tinkling sound can be heard in the movie Hereditary, is a reference to “Paimon”.
What will happen if I summon a demon Paimon?
It is never safe to invoke a demon, and we do not recommend summoning a demon after what happened when we tried to this spring. If you are planning to summon Paimon we highly advise you not to, as you can be attacked, possessed, face unwanted paranormal activity, curse your family, or even cause death to yourself and to others.