Copyright
A copyright is the (usually exclusive) right to copy, perform and distribute a work that is an original expression of a idea for a limited period of time. The owner of a copyright can be an individual, a collective or a corporation. The default owner of the copyright is the creator of the work; however, under United States law, copyright can be transferred or, if the creator was creating his work within the boundaries of a work-for-hire contract, belongs to his employer depending on the exact conditions of the contract.
In the context of the Transformers brand, Hasbro and TakaraTomy are the main copyright holders for their respective markets, and they often even act as representatives of the other one in their markets. For example, an American who violates the copyright of something that technically belongs to TakaraTomy will have to deal with Hasbro, who will act on TakaraTomy's behalf. Since most official Transformers-related works are specifically created under work-for-hire conditions, there are very few relevant things Hasbro and/or Takara don't hold the copyrights to, and they will try to amend that as well.
A copyright is not the same thing as a trademark. Since copyrights affect original expression of ideas, it is generally impossible to "copyright" a name, term or slogan, otherwise the simple act of "copying" (i.e. writing it down in a public venue, such as an internet message board) or "performing" it (i.e. saying it aloud in public) would amount to copyright infringement. Names, terms and slogans are protected as trademarks, which are only relevant in commercial contexts. Graphics and logos can be protected as both trademarks and copyrights. Unlike trademark infringement, copyright infringement can be committed by anyone; however, unlike trademark infringement, where the owner has to act as he might otherwise lose his trademark, it is up the owner of a copyright to decide whether he wants to pursue a particular instance of infringement or not. Compared to other companies, Hasbro and TakaraTomy have traditionally shown to be very lenient in this regard when it comes to taking legal actions against their own fans.
Copyright history
Modern copyright basics
Any time an original work is created that is an expression of one or more ideas, it is automatically protected by copyright. Ideas themselves cannot be copyrighted; for example, the idea "a robot that transforms converts into something else" cannot be copyrighted by itself, neither in terms of toys (anyone can create their own transforming toy robots without necessarily committing copyright infringement) nor fiction (anyone can write a story that includes transforming robots without necessarily committing copyright infringement). It is the specific expression of this idea that will be covered by copyright. The limitation for whether something is specific enough to count as aon original work covered by copyright or not is known as the threshold of originality'. For example, Generation 1 Optimus Prime's toy is protected by copyright, as is the backstory of the Transformers lore as originally developed by Marvel (alien robots from the planet Cybertron) and the specific stories told in comics, cartoons, video games and movies. What matters are not specific details by themselves, but the work as a whole. The more similar someone else's work is to these specific works, the more likely he will be found guilty of copyright infringement. The more vague the similarities are, the less likely he will be convicted. (It's not really possible to quantify the similarities in percents, though.)
The default owner of a copyright is the creator of the work. If a work is created as a group effort by several people, they share the copyright to the work, or hold the copyright to certain parts of it. For example, if Jim composes a song and Bill writes lyrics to go along with the tune, Jim owns the copyright to the melody (which includes the right to reproduce written notes!), whereas Jim owns the copyright to the lyrics. If they shared the workload for one or two steps, they share the copyright and need to reach an agreement when it comes to releasing or licensing their shared work. It is also possible to create a work under a work-for-hire contract for a company, which is the default in the American entertainment industry (creator-owned works are the exception rather than the rule). Anything created under the conditions of that contract is copyrighted to the company. When Hasbro assigned Marvel to develop a backstory for the then upcoming new Transformers series, Marvel was working under a work-for-hire contract for Hasbro, and Marvel's employees were working under a work-for-hire contract for Marvel. That means any stories, characters and concepts they created within the boundaries of their contracts were automatically copyrighted to Hasbro, not to Marvel or the individual creaturs. Marvel tried to circumvent that eventuality for a few characters due to a loophole in the contract, however (see below for more details).
