Basically, Articuno comes from a world where the Legendary Pokemon possess a human appearance to walk around the world and see how humans are behaving towards pokemon.
They also possess a mid form between human and Pokemon that they use when they want to fight with not full power. They still can understand what the Pokemon are saying and some of the pokemon even can notice that the Legendary Pokemons are in front of them as humans.
Though, as humans, they do not have their powers, that's the reason why they have to change forms. Once in a while, they gather together to discuss about everything.
His canon relationships are mostly with Moltres, Zapdos, Lugia and Mew. Sometimes with Suicune but nothing else. He doesn't talk too much to begin with :|a
Any questions goes here!