This is the section were I sound anal about the inconsistoncies in the Mario series. If it seems I'm nitpicking, it's because I am. All of this is as accurate as possible, using the games as the firt source, and other sources only when necesary.
Naming
The Mario Bros. consist of Mario Mario and Luigi Mario. They are the Mario Brothers because their last name is Mario. This is why it isn't the Luigi brothers. (Note: This has been confirmed by Miyamato-san himself)
The character in the original DK was originally refered to as jumpman when the game was in preproduction (some Japanese translation no doubt). By the time the game came into production in the US, though, the character was known as Mario. Therefore, it is acceptable to refer to Mario or jumpan as being the star of DK. However, the main character in DK3 is not Mario, but an exerminator known as Stanley the Bugman.
Toad is the royal mushroom retainer of the Mushroom Kingdom. Not all the little mushroom guys are "Toad", they are other citizens of the Murshroom Kingdom. Everyone calls them Toad anyway (Go fig). They might all look the same to us, but I'm sure theirs slight differences to tell them apart =)
The princess' name is Princess Peach Toadstool. The first name is Peach and the last name is Toadstool. That is why she is called Princess Peach in Japan and the letter at the beginning of SM64 is signed "Peach". Similarly, it is King Bowser Koopa. The first name is Bowser, and the last name is Koopa. This settles the double name issues.
The name Yoshi refers to the one specific, green dinosaur that Mario saves in SMW. The term "Yoshi" also refers to the whole species of multi-colored dinosaurs. There is only one "Yoshi" though. (confused yet?) The other Yoshi's (besides the main green one) are often called Yoshi's "cousins" although I don't think this is in the traditional, family relationship, but more like a general title (e.g. "father" used to refer to a priest). The baby Yoshi's found in eggs are not all children of the one, green, "Yoshi", but rather, babies of one of the Yoshi species of dinosaur. Understand? I didn't think so. But that's as clear as I could make it.
Settings/Storylines
Who Mario's parents are is unclear. Although the stork gives the bros. to a family in a Mushroom house at the end of YI, almost every other storyline (game or otherwise) suggests they were not born in The Mushroom Kindgdom, but rather in Brooklyn, then transported to TmK. Even though the "mushroom parents story" comes straight from a game, I find it hard to align with some games like DK, MB, and Wrecking Crew, so I'll leave the issue of the bros. past unsettled.
The true "Mushroom King" (i.e. Peach's father, nto the 7 kings in SMB3) is never mentioned in the games. He only takes form in the Nintendo Adventure System comics as a sort of ignoramus, who is basically just a figure-head, while the Princess does all the real ruling. It's as good an explanation as any.
The Mario bros. have been presented as plumbers, construction workers, and even demoltion workers at various points in their pre-princess-saving career. I like to think of them as general contactors, doing all sorts of work around the home from time to time. That's just my opinion though. The games stay away from Mario's occupation after SMB.
SMB take place in the Mushroom Kingdom. This is the gateway to the Mushroom World, where SMB3 take place. Each "world" in SMB3 is a different country of the Mushroom World. SMRPG also takes place in the Mushroom World. Although all three (including SMB2 in Japan) have a Mushroom Kingdom, none of them look the same. Maybe the kingdom's so big they all take place in different sections of the Mushroom Kingdom. It's just one of those unexplainable things =).
SMB2 is totally outside of the storyline of SMB and SMB3. It takes place in Sub-Con and is not made by the Mario team. It was originally Japanese game called Doki Doki panic with Indian characters. The programmers slapped Mario characters in there and bam, a new game. This is why none of the old SMB enemies are in it. SMB2 in japan actually picks up where SMB left off, and has similar play to SMB. It was released here in SM all-stars as the "lost levels". Strangely enough, the further Mario games retain some SMB2 (U.S.) enemies, which must seem new to the Japanese gamers who haven't played it.
In a similar way, SML was not made by the Mario team. It was not supervised by Shigeru Miyamato. This is why it has differences from the other Mario's, such as hearts instead of 1up mushrooms and strange enemy names. It takes place in Sarasaland, so the differences are forgivable storylinewise (as it's a totally different place)
Super Mario World take place in Dinosaur Land, which, coincidentally, has eight sections for the Koopa Kids to take over, as did SMB3 =). Yoshi's Island is one of these sections of Dinosaur Land. It is also the setting of Yoshi's Island (Duh) but has a lot more areas than the SMW Yoshi's Island, presumably, because it is set earlier than SMW.
SML2 take place in Mario Land, which has been turned to Wario Land by Wario. What is Mario land? How'd Mario get a land? Where is this land? Who knows. Maybe he got so much money from all those coins he bought his own land. SML3 take place place on Kitchen Island. I don't know how they got a statue of the princess there (in the ending), but, eh, whatcha gonna do.
Disregard any storylines put forth by books, TV shows, or movies featuring the bros. They are all so mixed up it's not even funny. Trying to connect the games story and Hollywood's will give you a headache, so just forget about it.
Spin-off character relationships
Wario's relation to Mario is very unclear. Some stories say that they're childhood chums (the NP comics for instance) some say their brothers (Wario being the evil twin) and I've even read one account saying Wario comes from another dimension. The similar naming (changing an "M" to a "W", how original) would be odd...unless they have some sort of family connection, but we can't know for sure. After the events of SML2 (and the ending of SML3) Mario and Wario part paths, and Wario makes quite a few cameos. In my opinion, Wario isn't really evil (Not in the way Bowser is) but his extreme greed leads him to do horrible things. I can't think of one "bad" thing he's done that wasn't prompted by money (Except in the inexplicable Wario's Woods)
Yoshi is a dinosaur that lives on Yoshi's Island in Dinosaur Land (with a summer home in Yos'ter Isle in The Mushroom Kingdom (SMRPG)). He is NOT Mario's pet (Neither is Poochie, while I'm on the subject). While Yoshi and Mario have had a special bond since the events in Yoshi's Island, it is not an owner/pet relationship at all. Yoshi helps Mario because in SMW he's also mad at Bowser (for trappnig him and all of his kind in eggs) and because Mario saved him.
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