Mario, Nintendo's biggest star, is also a playable character in all Mario Tennis games! His style is almost always All-Around, along with Luigi. His first appearance in Donkey Kong, over 32 years ago, has made him the main character for nearly every game, which is also shown in the Mario Tennis series. He is never an unlockable.
Mario's first appearance in a Mario Tennis game, as it was the first game of the MT series. Mario's Tennis is one of the only 3 Mario games to be released on the Virtual Boy. Mario was very basic, along with his friends, and they were just playing a classic game of tennis.