Zeus, the king of the Greek gods, was involved in most of these strange ancient births of mortals or humanoid gods. Zeus' propensity to show up on a mortal woman's doorstep in disguise is legend, so to be on this list, there has to be something more.
Note: There are plenty of other, stranger births involving animal forms, including Aristotle's theory of the spontaneous generation of flies from animal dung, but that's for another list....
Athena spent most of her gestation and childhood in papa Zeus' skull. When it was time for her to emerge, fully-armed, Zeus had to summon Hephaestus, the blacksmith god, to help with his pounding headache. An alternate version of the birth story has Prometheus
cracking the skull with an axe. This second version works better with one of the other strange birth stories.
How did Athena come to be in her father's skull? When the Oceanid Metis [see nymphs] became pregnant, Zeus swallowed her (and her fetus) to avoid an ominous prophecy: that the offspring of their union would be greater than Zeus.
Aphrodite was the goddess of love and beauty. In other pantheons, love and war are dual aspects of a single goddess, but the classical Aphrodite wasn't much of a warrior. When she tried to help her favorites in the Trojan War, she was injured. That doesn't mean she isn't associated with violence. She was born from the foam that rose up from her father's castrated genitals. After Cronus had severed them, they were tossed into the ocean. That's why Aphrodite is often shown emerging from the waves.
Zeus impregnated another woman, Semele. This time she was a mere mortal. When Hera found out, she wheedled her way into Semele's confidence so she could persuade Semele to ask Zeus for a favor. He was to reveal himself in his full splendor. Hera knew that it would be too much for Semele, and it was. Semele burned up at the sight of Zeus' radiance, but before she was consumed by fire, Zeus snatched the fetus and sewed it in his thigh. When Dionysus was ready to be born, for a second time, he came from Zeus' thigh.
Of course the most famous ancient human beauty had to be born under exceptional circumstances. It is just as inevitable that her father Tyndareus was not her biological sire. How Zeus managed to impregnate her mother is subject to dispute. Either Zeus as a swan impregnated Leda [see Leda and the Swan
] or Zeus impregnated Nemesis
while she was in goose form. In any event, Helen was hatched, not born, from either a swan or goose egg.
Helen's twin sister was Clytemnestra, the biological daughter of Tyndareus. Their twin brothers were the Dioscuri, Castor and Pollux, Castor, the son of Tyndareus, and Pollux, the son of Zeus.
Public Domain. Courtesy of Wikipedia
There's a term for this special kind of birth: heteropaternal superfecundation. It may also apply to the Dioscuri (the twin brothers Castor and Pollux). Alcmene was Heracles and his brother Iphicles' mother, but on the same night that she was impregnated by her husband Amphitryon, Alcmene had earlier been impregnated by Zeus disguised as Amphitryon. Thus Heracles and his brother were born at the same time, as apparent twins, but very different in capacity.
Keightley's Mythology, 1852.
Hera and Zeus were not only the married king and queen of the gods, but brother and sister. There seems to have been a healthy dose of sibling rivalry between these two. In Hesiod's Theogony, Hera is angry at the birth of Athena. To show Zeus that she was just as good as he was, she decided to produce an offspring all on her own. Unfortunately, she had a disadvantage in the spouseless production of a child. Zeus had actually mated with Metis and merely absorbed the conceived fetus. Hera produced Hephaestus entirely on her own and, perhaps as a consequence of missing DNA, he came out misshapen or lame.