Yoshi (sometimes specified as Green Yoshi) is one of the heroes of Mushroom World and an ally of Mario. He is a member of the Yoshi race and has aided his brethren in saving their homeland on multiple occasions. Yoshi has also saved other kingdoms from the villain Bowser as well. In his youth, Yoshi managed to rescue and protect Baby Mario and Baby Luigi from the wrath of Kamek and the Koopa Troop. All the Yoshi's are native to Yoshi's Island and live at Yoshi's House
Yoshi first appeared in Super Mario World, when Bowser launched his biggest assault yet against Dinosaur Land. To eliminate the threat of Yoshi, Bowser magically encased the green dinosaur and his friends in Yoshi Eggs. Many of these eggs were given to Bowser's own children, the Koopalings, to be watched over. Fortunately, for some reason, Green Yoshi's egg escaped the confines of one of the Koopalings' castles. Instead, Yoshi's egg prison wound up in a forest of Yoshi's Island. If Mario is hit while riding Yoshi, the dinosaur will yelp and run off scared and turn around when it hits something. Only able to be reclaimed if Mario hops back on. After defeating Bowser and the Koopalings, Mario, Luigi, Yoshi, and Peach return will all the eggs to Yoshi's House to watch them hatch into newborn, baby Yoshi's..
There are four colors of Yoshi. Green is the most common color and can perform special abilites when it swallows different colored shells. Green shell does virtually nothing except be spit out. Red shell lets yoshi spit fire. Blue shell lets Yoshi sprout wings and fly. Yellow lets him ground pound.
Red, blue and yellow Baby Yoshis can be found in Yoshi Eggs in the Star Road levels(in the gba version of Super Mario World you can find these colored yoshis in other places in dinosaur land) which can be fed to transform into adult colored Yoshi's, all of which can use their color-coded power up no matter what shell they eat, plus the power-up of the shell. For example, A blue yoshi swallows a red shell, so now it can fly and breathe fire. (but if you have a green Yoshi you have to hold that colored shell in your mouth to obtain that power.)
Although this move was not available yet in Super Mario World, in future games Yoshi has the "flutter jump" ability. This allows Yoshi to stay in the air longer and reach higher heights.