Toad is a recurring character in the Mario franchise, designed to accompany Princess Peach and protect the Mushroom Kingdom. He also regularly helps Mario and his friends.
He's one of the oldest characters of the franchise having first appeared in Super Mario Bros. in 1985. He is subsequently found in the vast majority of games, and even sometimes as a playable character as in Super Mario Bros. 2 or Super Mario 3D World.
Cheerful and optimistic by nature, he is also very fearful and panics easily when Princess Peach is in danger. He is very close to Toadette, although the nature of their relationship is quite unclear.