An Espeon is extremely loyal to any trainer it considers to be worthy. It is said to have developed precognitive powers to protect its trainer from harm.
Espeon's name is derived from ESP, or extra-sensory perception, a branch of psychic abilities. Eon was the proto-type for Eevee, Espeon's pre-evolved form. Espeon's Japanese name is probably derived from the fact that it's forked tail looks like a capital letter "F".
It appears to be based on legend of the nekomata, also known as bake-neko. Nekomata are mysterious two-tailed goblin cats. Simultaneously, Espeon also appeares to be based on an Egyptian goddess of the sun Bast, who was typically depicted with the head of a cat.