Boorish cannibals contrast with civilized Greeks in mythology except when it's the Greeks who prepare the ineffable dinners.
Medea was a horrible mother because she killed her children, but at least she didn't kill them secretly and then serve them to their father at a "reconciliation" feast, as Atreus did. The cursed House of Atreus actually contains two instances of cannibalism.
A story from Ovid's Metamorphoses that is singularly nasty involves rape, disfigurement, and imprisonment, with cannibalism as revenge.
Not himself a cannibal, Tantalus
shows up in the Nekuia
suffering eternal torture in the Tartarus region of the Underworld. He appears to have committed more than one transgression, but the worst is providing the gods with a feast for which he stews his own son, Pelops
. All the gods except Demeter
immediately recognize the scent of the meat, and refuse to partake. Demeter, distracted by her grief over losing her daughter Persephone, takes a bite. When the gods restore Pelops, he lacks a shoulder. Demeter must fashion one for him of ivory as a replacement. In one version, Poseidon
is so enamored of the boy that he takes him away.
The reaction of the gods to the dinner suggests they didn't condone the eating of human flesh.
Atreus, an unintentional cannibal, was a descendant of Pelops. He and his brother Thyestes both wanted the throne. Atreus possessed a golden fleece that conferred the right to rule. To get the fleece, Thyestes seduced Atreus' wife. Atreus later retrieved the throne, and Thyestes left town for some years. During his brother's absence, Atreus brooded and plotted. Finally he invited his brother to a reconciliation dinner. Thyestes came with his sons, who were strangely absent when the meal was served. When he had finished eating, Thyestes asked his brother where his sons were. Thyestes took the lid off a platter and displayed their heads. The feud continued.
3. Tereus, Procne, and Philomela
Tereus was married to Pandion's daughter Procne, but he lusted after her sister Philomela. After persuading Philomela to come with him to pay her sister a visit, he locked her in a secluded, guarded hut, and raped her, repeatedly. Afraid she might tell someone, he cut out her tongue. Philomela found a way to alert her sister: by weaving a story-telling tapestry. Procne rescued her sister and after seeing her, she decided on the best way to get revenge (and prevent the line of abusers from continuing). She killed her son, Itys, and served him to her husband at a special feast just for him. After the main course, Tereus asked that Itys join them. Procne told her husband the boy was there already -- inside him and showed the severed head.
The oldest daughter of Agamemnon, leader of the Greek forces headed to Troy, was Iphigenia. She was brought to Aulis, under false pretenses, in order to be a sacrifice to Artemis. In some accounts, Iphigenia is spirited away and replaced by a deer just at the moment Agamemnon kills her. In this tradition, Iphigenia is found later by her brother Orestes whom the Tauroi expect her to kill as a sacrifice to Artemis. Iphigenia says she is taking Orestes to be cleansed and so avoids actually making him a sacrifice.
Sacrifices in Greek mythology meant a feast for the humans and bones and fat for the gods, ever since Prometheus tricked Zeus into picking the richer looking, but insubstantial offering.
Polyphemus was a cyclops and son of Poseidon. When Odysseus entered his cave -- apparently breaking and entering and helping oneself to the contents of the frig was okay in those days -- the giant with one round eye (soon to be rolling on the floor) thought the group of Greeks had presented themselves to him for dinner ... and breakfast. Grasping one in each hand, he smashed their heads to kill them, then dismembered and chomped down. The only question is whether the species of cyclops is close enough to human to make Polyphemus a cannibal. I don't think the Greeks differentiated as unique races those whose shared ancestry went back to the anthropomorphic gods, so I've included this awful episode from Book IX of the Odyssey
In Book X of the Odyssey, the companions of Odysseus in their 12 ships land at the citadel of Lamus, Laestrogonian Telepylus. It's unclear whether Lamus is an ancestral king or the name of the place, but the Laestrygonians (Laestrygones) live there. They are giant cannibals whose king, Antiphates, eats on sight one of the the scouts Odysseus sends out to learn who lives on the island. Eleven ships had moored in the harbor, but Odysseus' ship was outside and separate. Antiphates summons the other giant cannibals to join him in smashing the moored ships so they can then make a meal of the men. Odysseus' ship alone gets away.
Public Domain; courtesy of http://www.ibiblio.org/wm/paint/auth/goya/
Cronus sired the Olympians Hestia, Demeter, Hera, Hades, Poseidon, and Zeus. His wife/sister was Rhea. Since Cronus had ruined his father, Uranus, he feared a child of his would do the same, so he sought to prevent it by eating his children one at a time when they were born. When the last was born, Rhea, who didn't much care for the loss of her offspring, gave him a swaddling-wrapped stone named Zeus to swallow. The real baby Zeus was reared in safety and later returned to overturn his father. He persuaded his father to regurgitate the rest of the family.
This is another case of "is this truly cannibalism?" As is true elsewhere, there's no better term for it. Cronus may not have killed his kids, but he did eat them.
Rise of the Olympians
The other Titans
besides Cronus shared with him a taste for humanoid flesh. The Titans dismembered the god Dionysus when he was just a baby, and ate him, but not before Athena rescued his heart, which Zeus used to resurrect the god.
Public Domain. Courtesy of Wikipedia.
In The Prose Edda
, Attila the Hun, the Scourge of God, is a monster, but hardly less than his wife, who shares with Procne and Medea the status of maternal son-slayer, and with Procne and Tantalus, a gruesome taste in menu selection. The character of Atli, with no heirs left behind, is mercifully slaughtered by his wife after finishing his unholy repast.