Yoshi

Yoshi is a green dinosaur and a main antagonist in the Mario and Yoshi series. He appears to have a saddle on his back which allows Mario to hop on and ride him. His first debut was in Super Mario World, of which he went with Mario to save his Yoshi Friends. The first game he appeared in as a main character was Super Mario World 2: Yoshi's Island, even though it might be noted that it could of been a different Yoshi.

Super Mario World
Yoshi's first appearance is in Super Mario World. He was trapped inside an egg by Bowser. Then, Mario hit a block and he found Yoshi, who was currently hatching out of his egg. When Mario rides Yoshi he can make Yoshi eat enemys, or eat Koopa Shells, which gives Yoshi special powers. Yoshi does not go inside ghost houses, or castles.

Super Mario World 2: Yoshi's Island
This game is the sequel to Super Mario World, but it's in the past. Yoshi is walking around and  a baby falls out of the sky. Which happens to be Baby Mario! Now, Yoshi has to go on an adventure to save Baby Luigi and Yoshi's Island.

Yoshi's Island DS
Kamek and his Toadies are going around the world to kidnap babies! It is up to Yoshi, Baby Mario, and Baby Peach to save Baby Luigi, the babies, and Yoshi's Island!