Plato believed that humans were originally in pairs, joined to another by the backs, but were split by the Gods because we were too powerful.
Now we are doomed to wander the Earth
until we find
"condemning them to spend their lives searching for the other half to complete them"
According to Theosophy, God created androgynous souls, equally male and female. Later theories postulate that the souls split into separate genders, perhaps because they incurred karma while playing around on the Earth, or "separation from God". Over a number of reincarnations, each half seeks the other. When all karmic debt is purged, the two will fuse back together and return to the ultimate.
I really, REALLY like this idea.
I think I should have liked Plato.