He competed with Athena for the position of dominant god for the ancient Athenians. Both of them presented the city with gifts; Poseidon gave either the first horse or a saltwater spring, depending on which legend you believe, and Athena won by giving an olive tree.
In myths, he does not have one.
He doesn't had friends
There are too many to name, also myths do not always coincide. It is still undecided wether or not Theseus was a son of Poseidon.
the function of Poseidons temple was for Poseidons honor.
Rhea.
cronus
some myths are some arnet
Cronus and Rhea
Neptune
a trident
Triton
Rhea.