Trigun/WMG

Wolfwood is one of the carriers of the Will of D.
His ancestors were the last of the carriers, and joined the rest of the human colonists on the SEED ships. He happened to be on one of the ones that Rem saved.

Trigun takes place in Warhammer 40k
Remember, many planets have been lost track of in the colonization of mankind. The planet is barren and desolate, with only few areas of green, perfect for either a hardship colony or penal colony. To take this WMG one step further, the plants are not power sources per se. They are psykers that are having their powers harnessed for the normal humans. To take this even further, Vash and Knives are the two missing Primarchs! Oh, exploitable!
 * Primarchs? No no no, they're modified orks. They're plant based creatures with incredible powers and a rather simplistic view of the world.

Vash and Knives are Abyssals.
All the horrible things that have happened to Vash and his loved ones are the result of Resonance.

The Black Cat is God, and the events of Trigun are purely for its own entertainment.
No, seriously. Or it at least is some sort of super-cat. How else could you explain it showing up pretty-much anywhere, anytime, especially around such weird characters as Vash? It even seems to have a "You amuse me." look in some scenes. Plus, the cat's Japanese name is given as "Kuroneko-sama", which literally translates as "Black Cat God", can't get much more obvious than that. Really, it translates to "Black Cat Lady".

Kuroneko-Sama is Haruhi Suzumiya
Prove me wrong.

The reason Vash is so persuasive and people don't shoot him is because he has a mind/emotion control ability.
Anime-only, but consider that Legato has Vash's arm and he can screw with the minds of others. If the power comes from Vash's arm, does that mean Vash himself has the potential to have even greater abilities? Such as making people THINK they actually are doing what they want to, when in fact Vash is controlling them?

Gunsmoke planet is world of Wild Arms
Picture of Vash can be found as easter egg in one of games.But the way Gunsmoke functions is very simillar to Wild Arms world so Gunsmoke is this series ancient world

Vash doesn't know where meat comes from
It's been shown that Vash is not a vegetarian. Yet, he refuses to kill, and won't tolerate other people killing. One could say that maybe he doesn't think animal lives are as precious as a human's, but remember, in the anime, he refused to kill a giant killer sandworm that was about to kill him. So, Rem never told Vash where meat comes from, and he never found out on his own, so he probably believes that meat grows on trees or something.
 * Though in one episode, Vash does say "Farewell my friend...and thank you," while eating an egg.
 * Except, given his life on the SEED procreation would have come up while they were being studied. Eggs come from chickens not being fertilized but could have been, would fall pretty well into his outlook. Now I feel so bad for Vash :'(

Vash is Gunsmoke's reincarnation of Jesus
Or it could be Rem as she did die to save everyone on the seed ship.
 * Maybe Rem's a reincarnation of the Virgin Mary?

Gungrave is the earth from the Trigun Universe in the Past!
Here are my point for this: Now Where do Plants come from? SEEDS! Which was the name of the colonizing project? SEEDS! My Theory is that the Seed was the key element in the development of the Plants, and Gungrave 3 will narrate the evenets that led to the Earth needing to develop the Plants and colonize another Planet.
 * 1) There were some references to Trigun in the Gungrave anime and Videogame, but one of them was the existence of the Chicken creatures that they use for transport in Gunsmoke appearing as racing animals in Gungrave. Which suggests genetic engeneering taking place in that world.
 * 2) The Seeds. In Gungrave OD the group uses some sort of Seed Creature to t rack seed, this creature is kept in a bulb shaped glass (Just like the Plants in Trigun) and it had some sort of wings (again just liek the plants).

Trigun is a alternate universe made as a result of Edward Elric's attempt to bring his mother back.
first of,both vash and edward have yellow hair,red coat and they have a metal arm. Edward's transmutation sucked them into a alternate universe where they are roborn again as vash and knives.Al retains slight knowledge of being the armor,but due to the transmutation,his mind gets warped and sees humans as inferior beings since they are not as durable as his armor was.

Vash is older!Roxas from Kingdom Hearts II
During an accident Roxas somehow lost his memory and ended up in the Trigun universe, losing his memory except for some one with spikey hair and the color red (Axel). In an attempt to remember, he began styling his hair in a similar fashion and wore red. The accident made him clumsier and eventually making into Vash the Stampede when he grew up.

Vash is Jesus In Purgatory
He's a good guy, with good principles, who suffers like you would not believe. And then people go and die for his sake and principles, like. And then he wins anyway.

Vash is Bit Cloud's Father!
Look up their pictures and note the huge similarities between their appearences and how everyone saw them as lucky idiots early on before they proved themselves as legitimate badasses.

Plus: If Bit's mom was Meryl then he'd have her last name so his real name would've been Bit Cloud Strife, but he just goes with Bit Cloud to keep the name short and simple.

Vash and Knives are Time Lords.
One, because of the meme. And two, because there is a bit of logic to it. From what this troper could tell we were never directly told what Vash and Knives are, other than not human, or at least they didn't anime. It was implied they were found on another ship, so they could be aliens. And the plant technology is some sort of Time Lord tech like the TARDIS, thus explaining Vash's connection with it and how he refers to it as living. Yeah I know, crack theory.
 * So totally my thought too. Additional proof: they are at LEAST 107 years old (Episode 17), the Doctor in Doctor Who has been shown to have precise timing, aiming skills like Knives and Vash, Time Lords have telepathic powers which explains the thought connection between Vash and Knives, and Knives exhibits an ability like the Master's to control/hypnotize others, their I Qs are well above human IQ, and so much more. This is my personal canon.
 * It's explained perfectly clearly what they are in the manga, though. However, the manga is kind of an alternate universe, so...

Vash Is an Idiot Who Gets Occasional Strokes of Genius
That's my headcanon and I'm sticking to it. Basically, Vash isn't obfuscating stupidity. He really is that dumb, he just gets strokes of genius occasionally.