Buchanan is the male Eevee, later Espeon, attached to the team of Machalí sol Linaros as a Champion of Suocé.
See also: Ufeŭ
Buchanan is one of two Pokémon based off of the Umbreon part of the Author's Pokémon Soul Silver run, specifically the one from Bill's batch in Goldenrod. For a character concept he's regressed to the Eevee stage and evolved into an Espeon The other, “proper” Umbreon derived from this concept is Ufeŭ.
As a character, Buchanan is envisioned as a stern, analytic and clingy Espeon who would have built over time good experience finding the weak points in opponent formations and would usually give instructions to the team (or right out lead the strategy once Pokéteco is unavailable or retired). He would specialize in a role similar to that of a Synergist, creating fields of energy where his allies would be able to fall back to to receive various boosts or heal from enfeeblements, and would devise strategies to improve his own mobility so as to draw enemy fire away from eg.: Maekrite.
As a feline Pokémon with psychic abilities and knowing of the technique to teleport, he would be susceptible (and vulnerable) to Summon Cat.
He is named after Bill Buchanan, a character in the TV series 24 who took on the role of a leader and strategist for the protagonist counter-terrorist agency.