What is the legendary dog Pokemon?

Raikou, Entei, and Suicune are the legendary dogs.

Some consider Arcanine a legendary dog, but he is not part of the trio. the reason for this is that in an early episode, Arcanine was in the middle of a slate surrounded by Moltres, Articuno, and Zapdos. After the episode, it was decided that Arcanine was NOT a legendary dog.