“There are interesting correlations between myths across different traditions, links forged between Wales and Ireland in particular, but also persistent tropes shared by numerous cultures, including “tripleism”, which plays a key role not only in Welsh myth, but also in Macbeth’s trio of witches and old nursery rhymes. Threeness is 'an endemic part of British and European Iron Age and Roman provincial symbolism'.” — Otherworld Wales at TLS, discovered via Warren Ellis.
Relatedly: “During the Old Kingdom, the Sun god used to appear in three forms: at dawn called khepri (Ḫpr), at mid-day called Re (R‹) and at the sun setting called Atum ™...”
Let me just interject here by saying that this is clearly the basis for what we now know to be the three-act structure in storytelling.
“By the Middle Kingdom, trinity developed by merging three divinities together such as god Ptah-Soker-Osiris (Ptḥ-Sḳr-Wsir), who was regarded as single divinity in some texts by stating a single pronoun (di.f) or by stating plural pronoun (di.sn). The ancient Egyptians merged these three gods because they represented three stages; creation, death and afterlife, as god Ptah formed the creation, god Soker represented the necropolis and god Osiris represented the afterlife. Furthermore, during the New Kingdom in the Book of the Dead in chapter seventeen, the idea of the trinity was expressed by mentioning “Osiris (Wsir) was yesterday, current day is Hours (Ḥr) and tomorrow is Re (Ra)”.” — The Significance of the Number Three in the Ancient Egyptian Religion by May Ahmed Housny and Kholoud Ahmed Emara. Not the best written paper tbh (chalk it up to ESL), but some great information there. Like this bit of madness:
“The ancient Egyptians believed that the human identity was divided into two main elements: materialistic and spiritual. Our main concern will be directed to the spiritual elements as it comprises three main elements which were: Ka (k3): It is the sole companion which is born with the creation of the human being, Ba (b3): It is the spiritual entity that can move between worlds of living and death, Akh (Aḫ): it is the illuminated spirit in which the deceased wished to be resurrected in.”