ISIS = Demeter

From the always helpful librarian

1. Demeter and Isis

The Greek historian Herodotus 

explicitly wrote that Isis is 

the Egyptian equivalent of Demeter. 

They shared the closest theological connection

 due to their nearly identical mythological arcs:

The Search for the Lost Family: 

Just as Demeter wandered

 the earth in deep mourning looking for her

 abducted daughter Persephone,

 Isis wandered Egypt in grief

 searching for the scattered pieces of her murdered husband,

 Osiris.

Agriculture and Fertility: Both goddesses were revered as

 the ultimate providers of agriculture, law, and

 the gift of grain to humanity.

 During the Ptolemaic period,

 Isis was often depicted holding a cornucopia or ears of wheat,

 borrowing heavily from Demeter's traditional imagery.

2. Persephone and Nephthys / Isis-Thermouthis

Persephone's Egyptian equivalents shifted

 depending on her dual role as both 

a goddess of spring agriculture and

 the queen of the underworld:

Nephthys (Underworld Aspect): In the Egyptian underworld narrative,

 Nephthys is the sister of Isis 

and the wife of Set 

(the god of chaos/underworld elements).

 When Greeks looked at the divine pairs,

 they often viewed 

Isis and Nephthys

 as a parallel duo to 

Demeter and Persephone,

 representing the cyclical balance between

 the living world and

 the realm of the dead.

Isis-Thermouthis (Agricultural Aspect): The Egyptians 

worshipped Renenutet (Greek: Thermouthis),

 a cobra goddess of the harvest and fertility.

 Over time, she merged with Isis.

 Because Persephone represented 

the actual sprouting of the grain

 from the earth,

 she became deeply intertwined 

with this specific,

 agricultural aspect 

of Isis's daughterly expressions.

The Hellenistic Synthesis: Serapis 

The connection between these goddesses 

was solidified by the creation of Serapis,

 a composite god introduced by Ptolemy I Soter.

 Serapis combined aspects of Osiris and Hades 

(Persephone's husband) 

with Zeus and Dionysus.

 As Serapis became the supreme lord

 of the underworld and afterlife,

 his divine consort was naturally worshiped

 as a blend of Isis and Demeter,

 completely intertwining the Eleusinian 

and Egyptian mythologies.

If you want to explore further, let me know if you would like to look into:How Herodotus documented these similarities in his travelsThe specific temples in Egypt (like Alexandria or Philae) where these combined deities were worshipedThe role of Osiris as the Egyptian counterpart to Hades/Dionysus

From Wikipedia

Hesiod's genealogy

According to Hesiod, the children of Uranus and Gaia were

 Oceanus, Coeus, Crius, Hyperion, 

Iapetus, Theia, Rhea, Themis, 

Mnemosyne, Phoebe, Tethys,

 and Cronus.[2] 

Among eight of the twelve Titans

 there were four marriages 

between brothers and sisters: 

Oceanus and Tethys, 

Coeus and Phoebe, 

Hyperion and Theia,

 and Cronus and Rhea.

 The other two Titans, 

Iapetus and Crius, married with familiars

 who were not their sisters.

 Iapetus married his niece Clymene,

 the daughter of Oceanus and Tethys,

 while Crius married his half-sister Eurybia,

 the daughter of Gaia and Pontus.

 The other two Titanesses, 

Themis and Mnemosyne,

 married with their nephew Zeus,

 the son of Cronus and Rhea.

From Oceanus and Tethys 

came the three thousand river gods,

 and three thousand Oceanids.[3] 

From Coeus and Phoebe came Leto,

 another wife of Zeus, and Asteria.[4]

 From Crius and Eurybia came Astraeus,

 Pallas, and Perses.[5]

 From Hyperion and Theia

 came the celestial personifications 

Helios (Sun),

 Selene (Moon),

 and Eos (Dawn).[6]

 From Iapetus and Clymene came Atlas,

 Menoetius, Prometheus, and Epimetheus.[7]

 From Cronus and Rhea

 came the Olympians: Hestia,

 Demeter, Hera, Hades, Poseidon,

 and Zeus.[8] 

By Zeus, Themis bore 

the three Horae (Hours), 

and the three Moirai (Fates),[9] 

and 

Mnemosyne bore the nine Muses.[10]

While the descendants of the Titans Oceanus and Tethys,

 Cronus and Rhea, 

Themis, and Mnemosyne 

i.e. the river gods, the Oceanids, 

the Olympians, the Horae,

 the Moirai,

 and the Muses

 are not normally considered to be Titans, 

descendants of the other Titans, 

notably: Leto, Helios, Atlas, 

and Prometheus, are themselves 

sometimes referred to as Titans.