Tranquill is an avian Pokémon that resembles a pigeon.
Tranquill seems to have very strict requirements and a more serious nature, and can rely on their keen intuition and sharp vision to pursue the route, looking for their targets. But Tranquill are also very friendly, so it is not necessary for human to question about their loyalty. Tranquill seems to be having a spirit of pacifism, which may be a reason why humans believe them that they live in a kingdom full of peace.
Tranquill's name seems to be the word tranquil, meaning peaceful, which is also similar to what the dove represents. It also contains the word quill, writing utensils made out of primary-feathers from birds.