The one on the left is Athena, goddess of wisdom, daughter of Zues, born from Zues' brain, niece of Poseidon. The one on right is Poseidon, Lord of the sea, brother of Zues and Hades, uncle of Athena
They co-owned a coastal village. Having village under the care of two gods was too dangerous. Athena challenged Poseidon to a contest to see who would own the village alone. They decided that the gods would give the town a gift. Whoever's gift the townspeople liked more would get to own the village.
Uncle Poseidon, I challenge you to a contest!
The gods created their gifts to the village. Athena made an olive tree and Poseidon made a stream on the side of a mountain.
Here is an olive tree for the people of [unamed] village to enjoy!
Here is a stream of water for the people!
You should all choose Athena and her brilliant, useful olive tree!
And now the people had Athena as their leader and her olive tree that could be used for food, trading, wood for houses, and fire branches. Now, that's how the first olive tree came to be.