The Super Mario game series consists of hundreds of games spread across many gaming platforms. The series began in September 1985 and has sold 271 million copies from the main series alone.  There are also many sub-series spinoffs including the Mario Kart franchise, Mario Sports franchise, Paper Mario franchise, and Super Smash Bros franchise. For further reading check out the Mario Wiki
Mario Franchise CharactersThe Mario game series has thousands of characters between the many games, but some characters have appeared countless times in nearly every title. Here's a look at some of those characters.
Mario himself has appeared as a playable character in a good majority of the games in the series, some exceptions include Luigi's Mansion, and Super Mario World 2: Yoshi's Island. Mario along with many other Nintendo characters is portrayed by Charles Martinet, and is the most well known gaming mascot in the history of the industry.
LuigiWhile he's not usually as popular as his brother, Luigi still stars in his fair share of games. Luigi is unlockable in the recently released Super Mario 3D Land, and he stars in his own 3DS game Luigi's Mansion 2. He may not be as good as rescuing Peachas Mario, but his personality has become a fan-favorite.
Being the princess of a kingdom intent on kidnapping you isn't always an easy job, but Princess Peach always has Mario to rely on. Peach has been kidnapped in some form or another in nearly every game she's appeared in (with the exception of games like Mario Kart and Mario Party) and shows no sign of slowing down any time soon.
Although Bowser wasn't Mario's first adversary, he was certainly his strongest. After Donkey Kong decided to turn good, Bowser took over the role of the baddest of all bad guys and began kidnapping Mushroom Kingdom politicians. Bowser has appeared as the antagonist in most Mario platformers, and has also played the role of antagonist and protagonist in the Mario RPG series.
Spending his days carrying around Mario and his pals can become tedious after a while, and so on occassion Yoshi has his own adventures without Mario. Yoshi's first appearance on Nintendo 3DS was in Mario Kart 7 in which he was one of the eight starting drivers.