They even have TV shows about them! The Super Mario Bros. Super Show!, the Adventures of Super Mario Bros. 3, and Super Mario World. The last one has Yoshi.
Although the "main hero" role is normally given to Mario, there were a few games where Luigi is in the spotlight. Figuratively speaking. There is no real spotlight, it is just a term used to describe someone is the main hero. Anyway, here is a list of the games.
- Mario is Missing! - In this game Mario scouts ahead in Bowser's Castle, only to become Bowser's prisoner. So Luigi must explore the castle, look for Mario, and defeat enemies along the way. In most versions Mario AND Luigi combine their strength and throw Bowser so far away that he lands at the South Pole. However, in the PC version, instead of throwing him, the Mario Bros. just take off Bowser's shell, so we see his underwear. He wears boxer-shorts with yellow ducks dotting them. Either way, Bowser is humiliated and the Mario Bros. save the day (Bowser was opening a portal to the real world).
- Luigi's Mansion - In this game Luigi wins a contest and the prize was a five story mansion. Awesome, right? Anyway, the only downside is that the house has hundreds, maybe thousands, of ghosts. And it just so happens that Luigi's worst fear is ghosts. Yet again, he has been afraid of most things. He's afraid of spiders and anything that goes bump in the night. No not literally, it is just a term used to describe something that might ambush you when the sun goes down. Anyway, Mario decides to set up a party in the new mansion. He went in there one hour before Luigi got there, and a creepy part is that he never came out. As Skales from Ninjago would say, "Spooky!". Even though when he says it, he makes a hissing sound at the beginning. Because he is half snake. Anyway, Luigi meets a scientist named E. Gadd. Gadd give Luigi the Poltergeist 3000, a vacuum cleaner shaped ghost hunting tool. After defeating all but one ghost in the mansion, Luigi meets the King Boo. The King Boo is a giant Boo with a crown on his head, a long blue tongue, and eerily red eyes. So Luigi fights King Boo, who, by himself, is weak and easy to defeat. But he cheats by summoning Bowser. But he still loses, is sucked into the Poltergeist, and all that remains of him is his crown (which can be collected). And Mario is freed from Picture Prison. I should probably mention that Mario was stuck inside a painting up until now.
- Luigi's Mansion 2 - A direct sequel to to Luigi's Mansion. Instead of ghost hunting in one mansion, you get to go ghost hunting in five mansions!!! No two mansions are the same. E. Gadd is now doing research on friendly ghosts. These ghosts are different from the ones in the first Luigi's Mansion because all the ghosts in that game are aggressive. The secret is the Dark Moon, which has a calming effect on ghosts. But King Boo blows it up. And the ghosts become extremely hostile. But Gadd has a plan B. At the Mario Bros.'s house, Luigi was watching TV and his show was interrupted when E. Gadd appears on the screen. Gadd activates a teleporter, and next thing you know, Luigi is standing right beside Gadd. E. Gadd then gives Luigi the ultimate ghost hunting tool, the Poltergeist 5000!!!! It still has the vacuum cleaner shape, but it has a strobe-light. Which is needed to blind ghosts. A blinded ghost is a defeated ghost. It also has a blow function, and along with the suck function, both of these features can interact with pretty much everything in a room. After defeating all but one ghost in the five mansions, King Boo appears and challenges you to a dual. And King Boo somehow kidnapped Mario and trapped him in ANOTHER painting. After beating him, King Boo gives up the final piece of the Dark Moon, some Toads rebuild it, and all the ghosts become friendly again.
It is worth noting that Bowser has appeared in almost every Mario Bros. game. In a couple games Bowser would have to team up with Mario to take down a bigger threat. In Mario & Luigi: Bowser's Inside Story, Bowser accidentally ate both Mario and Luigi, but they avoided being digested and have an adventure in Bowser's stomach and, later on, the inside of his entire body. Meanwhile, Bowser has to deal with Fawful, a mysterious character that (just like Bowser) wants to rule the Mushroom Kingdom. At one point in this game, some Boos force-fed Bowser a large amount of ham (and cake. And bacon. And about a thousand other foods I could name.), resulting in Bowser getting extremely fat. It is shown every now and then in most games that Bowser has fallen in love with Princess Peach. Like in Super Paper Mario, Bowser and Princess Peach were forced to marry thanks to this villainous character (I forgot his name though). While Peach hated this scene, Bowser was enjoying this scene. Bowser kept calling Peach his "wife" throughout the game after the forced marriage. Lets not forget that Bowser is a turtle-like monster, and that Peach is a human. That would be a little strange. And in both Super Mario Galaxy games, Bowser wanted to make Peach his queen. And In Super Mario Sunshine, Bowser told his son, Bowser Junior, that Peach was Bowser Junior's mother, and that Mario kidnapped Peach. At the end of that same game, Bowser Junior revealed that he knew since the beginning of the game that Peach was NOT his mother. Bowser only told his son that Peach was his (Junior) mother because it would seem like a complete family. Or so I believe.
If you have played any game with Mario AND Yoshi in it, you would have noticed how easily Mario controls a Yoshi should Mario ride one (like a horse). Have you ever wondered why? If so, then read this paragraph about how Yoshi, Mario, and Bowser first met and the reasons why Bowser and Mario fight all the time. In Super Mario World 2: Yoshi's Island, Kamek (a Magikoopa that is Bowser's right hand man as well as his nursemaid.) predicted that when Bowser reaches adulthood, Mario will ruin Bowser's plans for everything Bowser tries to do. Kamek decided to prevent that from happening by attacking some storks. Two of these storks were carrying Mario and Luigi when they were babies. And guess who managed to get his cute dinosaur hands on Baby Mario? Yoshi!!! Yoshi spends pretty much the whole game carrying Baby Mario on his back. near the end of the game, Yoshi and Baby Mario meets Bowser when HE was a baby. And ever since the two toddlers met, Bowser and Mario became rivals. First they argued over who gets to ride on Yoshi's back. Then they started competing for Princess Peach's affection, and that brings it up to the present day Mario Games where Bowser tries to make himself king of the Mushroom Kingdom (and in the Galaxy games, the whole Universe). And Yoshi would lend a cute dinosaur hand to help Mario defeat Bowser. And in every boss in the first Yoshi game, Kamek would super charge the boss, just to get rid of Mario and Yoshi. Kamek actually never worried about Luigi helping Mario, as Luigi was never seen in Kamek's vision of the future. Even though Kamek did use Baby Luigi as bait to lure Baby Mario and Yoshi into the the final boss level (which was a trap).
And here is a Character Gallery!!!! NOTE: All images are from the Super Mario Wiki.
This is Mario, in his famous jumping
This is Bowser. He can use magic powers and
can breathe fire.
This is Yoshi. He is a cute dinosaur
(with cute dinosaur hands).
Princess Peach. The current ruler of
the Mushroom Kingdom.
Luigi. Mario's younger brother
as well as Mario's right hand man.