Unless you’re the newest of nubs in Hellenic polytheism (in which case, you shouldn’t start with this blog, you should start with most of the info I have under “Hellenismos Resources”), the you probably already know that the Triple Goddess of Maiden, Mother, Crone is pretty much an invention of Robert Graves. Graves is also author of The Greek Myths, typically published in two volumes, and it’s full of some really weird ideas that are largely dismissed by Classics scholars and pseudo-etymology that seems more based on the kind of “feels” and “truthiness” that Kaldera and/or Schwartzstein lept to in Urban Primitive than any sort of scholarship of the ancient Hellenic dialects. Now, as mythological poetry, it’s no more valid or invalid than some of the “UPG-based” stuff I’ve read from people less-read on the Internet, and he certainly writes better than most of them. That said, the idea of Persephone, Demetre, and Hekate being unified in some Maiden-Mother-Crone tryptich is purely from Graces’ own imagination and the only basis for it in Hellenic mythology —if you squint— is the fact that all three play a role in the mythology of the Elusinian Mysteries, but even then, Hekate is still clearly the “Maiden” She has always been in classical Greek thought. Yes, by some mythology, She is also Mother to Kirke and others, but the menopausal dowager of popular Neopagan religion is in no way a manner in which the ancient Hellenes depicted Hekate.
That said, the idea of goddesses in particular grouped together in triads certainly is an ancient concept, and was no stranger to the ancient Greeks. So, just from memory, here are all the triad deities in the Hellenic pantheon that I can think of –it might not be literally all of them, but oh well– and this is not counting groups of more than three, like the Pleiades or the standard Nine Olympian Moisai.
Moisai Titanades: The three “Titan” Muses; by some accounts, the Moisai Titanades are four in number with Melete being the only common name and Theoi Project says the two groups are essentially the same three plus one, but my own gnosis says literally all named Muses exist. Their names are Mnene (Memory), Melete (Practise), and Aiode (Song), and by some fragments, They’re the daughters of Gaia and Ouranos.
Moisai Apollonides (as per Eumelus fragment): Daughters of Apollon, They are Kephiso (of the river Kesiphus), Apollonis (Daughter of Apollon), and Borysthenis (Strength). I’ve found no narrative mythology about them, and only Borysthenis is named for a virtue of the creative process, though it’s easily arguable that Apollonis would embody much of the same command for music that Apollon Himself does.
Moisai Apollonides (as per Plutarch): Nete, Mete, Hypate –they rule, respectively, the lowest, middle, and highest octaves of the lyre. On a personal gnosis bend, this extends to the octaves of music, in general. While I have found no ancient narratives about this set, either, I have one in my draft folder; I’m not happy with it at all, but most of the stuff that I post in spite of thinking it’s complete shit seems to get kinda popular, anyway, so maybe I’ll post it some time, anyway.
Moirai: While there are certainly others named, and I do, too, believe I have knowledge that that not only are all named as Moirai are Moirai, but also Tykhe and Psykhe are among their numbers, classically only three are named: Klotho (She Who Spins our Threads) and Lakhesis (She Who Measures Our Threads) and Atropos (She Who Cuts Our Threads). The primary three are the daughters of Nyx, and the Moirai in general are believed to preside over all births, both mortal and Divine, dispense major life lots before they’ve ever happened, and even assign domain to the Deathless Ones.
Kharites: Again, many are named and I personally believe most, if not all of Them exist, but they’re typically depicted by ancient and modern eyes as a triad —while modern eyes tend to lean Them almost always in attendance of Aphrodite, there is no shortage of surviving ancient accounts of Them being worshipped outside of Aphrodite’s cult, and as I recall, one of Pindar’s accounts, they were worshipped alongside Apollon, and in Delphi and Delos, They (rather than the Moisai) were depicted in the hands of Apollon, and They have been depicted in ancient art as attending Hera, Dionysos, Hermes, Eros, the Horai, and the Moisai. Their worship originated in Boiotia, by way of the legendary king of Orkhomenos, Eteokles, who also numbered them as Three, but apparently, even by surviving ancient accounts, They weren’t named until later. The most common name of the triad of Kharites is usually Aglaia, Euphrosyne, and Thaleia.
Erinyes or Praxididai: The Erinyes, “murky ones”, avenging crimes against the gods, homicides, and abusive child-parent relationships. By some accounts in narrative mythology, They are assigned by Hades and Persephone to torture the damned amongst the dead. The Praxidikai, “avenging ones”, is a Boiotian grouping of three similar goddesses. Unfortunately, having interacted with these Goddesses minimally, I’m just going on gut here, but I personally approach these two names for the “sets” as a regional difference for the same class of goddess triad.
Erotes: You know, I almost left this other common triad out, cos a good three or four years ago, I just stopped thinking of this grouping as a triad altogether at the behest of Eros. There FAR are fewer extended names for the Erotes than there are for Kharites, but I dunno, somehow it’s easier for me to think of the Kharites, though They are far more than Three, as simply travelling in threes –maybe the spirit of Eteokles is simply overriding what would normally seem logical to me about that. That said, the most common triad of Erotes tends to be Eros, Himeros, and Pothos. This is also an unusual triad, as triad deities tend to overwhelmingly be female in nature, and this seems to be a habit that even extends into the Celtic and Norse pantheons.
Again, going only by memory, the only other male triad of deities I can think of are the judges of the Dead in Hades’ employ. By Platonic accounts, the “demiurgic triad” of Zeus, Poseidon, and Hades is a rather loose one, in that unlike the others that are usually depicted in art as almost inseparable, They’re seldom depicted together in that way (another reason I hesitated toward adding the Erotes, as Eros Himself, as well as others associated with that grouping, are just as, if not more often, depicted without the triad).