Not all goddesses who engender offspring are the Mother Goddess. Many female deities have been worshipped in the past: Ishtar (Inanna) in Mesopotamia, (Aphrodite in Greece), is well-known. In Scandinavia a female goddess was probably worshipped during the Bronze Age and (probably) later in Norse mythology as Freya. Sarasvati and other female goddesses in different pantheons may also be considered mother goddesses.
In the Aegean, Anatolian and ancient Near Eastern culture zones, the Mother Goddess was worshipped in the forms of Cybele (revered in Rome as Magna Mater, the 'Great Mother'), of Gaia, and of Rhea. In Crete one of her aspects was the Mistress of the Animals (Potnia Theron), the Triple Goddess who devolved into Persephone - Demeter - Hecate, Maiden (Kore), Mother and Crone. The Olympian goddesses of classical Greece eclipsed the Mother Goddess without ever really supplanting her. Her roles were divided among Hera, Demeter and Athena. Even the archaic Artemis of many breasts, as worshiped at Ephesus, retained some of her older divinity.
Information about the Mother Goddess can be found under all the linked entries.
The Mother Goddess is worshipped by Modern Wiccans and other Neo-Pagans. The mother goddess is usually viewed as mother earth.