Transformers is a line of robot action figures that transform from humanoid shapes to any number of not-so-humanoid shapes, from semitrailers to jets to cassette tapes to dinosaurs. Owned by Hasbro, Inc, the toyline was first introduced in 1984. Since then, it has gone on to spawn a number of different cartoons, comics, and movies. Originally aimed at young boys, the toyline is now also enjoyed by grown men (usually the grown-up young boys it was originally aimed at), grown women, and adolescent females, the latter most likely thanks to the 2007 movie.
Because of the many different Transformers continua (So much that one continua has even cataloged them), Transformers canon is hard to pin down—basically, as long as Hasbro approved it, it's canon for some continuum, and if two continua that are supposedly related contradict one another, both should be considered equally canon unless Hasbro says otherwise. Each continuum is split into several related but slightly different continuities, leading them to be called "continuity families" by the fandom. Characters, settings, and events are often subject to change. However, the basic premise of Transformers canon remains the same in all but a small handful of them.
The Basic Premise
The evil Decepticons and the heroic Autobots are pitched against each other in an all-out war between good and evil. Said war usually begins on their home planet of Cybertron, and more often than not makes its way to a certain blue and green globe known as Earth by the natives. There, humans help the giant robots wage their battles, usually siding with the Autobots, as the Decepticons tend to squish them without second thoughts.
Some Transformers continua are more popular than others, and thus are more used in fanfiction. A full list of continua and their relations to one another exists at the TFWiki, linked at the bottom of the page.
Generation 1 Continuity Family
The very first Transformers continuum ever, of which takes place in the Primax Cluster. It is made up of the toyline (duh), comic books, and, most notably, a cartoon series that lasted from 1984 to 1987. Other members of this continuity family include the less successful Generation 2 series that lasted from 1993 to 1995, as well as the Beast Wars series that lasted from 1996 to 2000.
The Japanese G1 Continuity has many more (though some questionable *cough cough* Kiss Players *cough cough*) sources of canon, and is not a member of the state-side Primax continuum.
Transformers: Robots in Disguise (2001)
Transformers: Robots in Disguise, taking place in the Viron Cluster state-side. Notable features includes it being a return to source for the Autobot/Decepticon conflict, with some Predacons joining the Decepticons, and the first instance of Optimus Prime having a supermode and combining with fellow Autobots, a trend that would continue through the next couple series.
It is known in Japan as Transformers: Car Robots, and is part of the Japanese Primax Cluster.
The Unicron Trilogy
Comprised of three anime series, Transformers Armada, Transformers Energon, and Transformers Cybertron, and takes place in the Aurex Cluster. It is named the Unicron Trilogy after the unifying theme of the threat of Unicron, a planet-eating dark god. Unusual in that while Energon follows Armada on the timeline as a sequel series, whether Cybertron follows after Energon or its place on the timeline is "off to the side" (so to speak) is debated. Notable for things such as Armada's incarnation of Starscream being possessed in an infinite number of badfics, Energon's notorious lack of quality, and the Cybertron dub being bashed by people who saw the Japanese version first in spite of the fact that on examination, it is of higher quality than Armada and Energon, and overall works better as a series than the original Japanese (so says TFwiki).
They are known in Japan as Transformers: Micron Legend, Transformers: Super Link, and Transformers Galaxy Force respectively, and takes place in same continuity stream.
Set in modern times in the Tyran cluster, this live-action movie is probably responsible for most of the teenage girl Transformers fans. A sequel came out summer 2009. The third was released in 2011. And the fourth in 2014. And the fifth in 2017. And a spin-off/prequel/reboot/whatever focusing on the Autobot hero Bumblebee in 2018.
A more recent version of the series taking place in the Malgus cluster It was formerly viewable on Cartoon Network. Unlike previous cartoons, it's actually enjoyable for adults to watch, as well as young children, as well as having a more Superhero theme. It lasted from 2007 until 2009.
Aligned Continuity Family
The most recent version of the series, designed by Hasbro to be the foundation of the franchise for the next decade. Starting with the War For Cybertron video game and continuing with the cartoon series Transformers Prime and it's sequel series, Transformers: Robots in Disguise (2015). It combines aspects from the other continua together in an effort to to form a more unified continuity possessing the best qualities of its predecessors.
There is also the "directed at younger kids" series Transformers Rescue Bots and its sequel series, Transformers: Rescue Bots Academy. It, unlike Prime and RID, stays out of the "good versus evil" battle between the Decepticons and Autobots and instead focuses on Transformers trying to protect a small, island town while trying to keep their true identities a secret.
The third season of Prime does not exist in the Japanese version, with Transformers Go! taking it's place. RiD is known as Transformers: Adventure in Japan, it is unknown if it occurs in the same timeline as the Japanese Prime.
Because the purpose of the Transformers toyline is, well, to sell toys, there are many, many, many, many more characters than those listed here. These are the ones most used in fanfiction.
Also, because Hasbro's aim, like most corporations, is to make as much money with as little effort possible, many characters have several different versions of themselves—colors, personalities, alternate forms, and abilities vary from continuum to continuum.
- Optimus Prime
- Ultra Magnus
- Air Raid
- Starscream (the undisputed little black dress of the fandom)
- Long Haul
- Sparkplug Witwicky
- Spike Witwicky
- Sari Sumdac
- Jack Darby
- Miko Nakadai
- Rafael "Raf" Esquivel
- Russel "Rusty" Clay
- Dusty Clay
Again due to the number of different continuities, Transformers fanfiction is quite varied. Oftentimes, writers will introduce characters who were prevalent in one continuum into another where they are never or rarely seen. Writers may also choose to further blend two or more continua together (which admittedly has happened in canon on occasion, as the many continuity families are considered to be different realities that all exist within a single multiverse... except for the Aligned continuity family; it's really complicated). It can get very confusing for those not familiar with the toyline.
Notable problems in Transformers fanfiction include bad slash (they're giant robots; they don't interact the way we do), interspecies romance (repeat: giant robots; falling in love with a human is unlikely... though it has happened in japanese canon, but we don't talk about that), and the occasional Mary Sue (available in both human and robot forms).
For further information on anything and everything having to do with Transformers, go to the Transformers wiki.