Transformers started in 1984 with the release of the first comics and toys for the G1 line. Hasbro started out by releasing in North America toys which had been available for a few years in Japan but had previously sold poorly in the the USA. The following year, the line was launched in Japan, where the American year one and two toys were smooshed into just one year of releases. Later in its life, the Transformers G1 line began producing new products which were specifically designed for it, ending (in North America at least) in 1990 amidst an avalanche of Micromasters and Action Masters.
In late 1992, Hasbro relaunched the franchise as "Transformers: Generation 2". In Europe, where Transformers had never disappeared, the new name simply started appearing on the boxes. Meanwhile, in Japan, 1992 was the last year of G1, with Operation: Combination wrapping things up. Japan saw no more Transformers until they started releasing toys under the G2 banner in 1995.
Like its predecessor, G2 began by re-releasing old toys. This time, they were toys and characters from G1 with new -- usually flashy -- color schemes and electronic sound gimmicks. TF:G2 gradually began introducing new product and introduced design innovations that are now often taken for granted such as ball-and-socket joints and lightpiped eyes. Some of the most well-reviewed Transformers of all time were created for this line. The Japanese version of G2 was much smaller, and included only new-mold toys.
Just a bit earlier, in 1991, Hasbro had finally achieved something it had wanted to do for many years: It bought out competing toy-maker Kenner. (Hasbro actually bought Tonka, of which Kenner was then a subsidiary.) It has been theorized (ie. it's not certain) that Hasbro took this action because, at the time, Transformers was on its way into the crapper and GI Joe was doing similarly poorly. Kenner had just won a bidding war for the Star Wars license, and Hasbro felt that they basically needed the license to avoid obselesence in the boys' toys market. So, they simply bought Tonka/Kenner out. As part of the restructuring that followed over the next few years, Hasbro in 1995 moved their lucrative boys' lines from their Pawtucket, Rhode Island headquarters to the Kenner offices in Cincinnati, Ohio. (This happened just in time to throw BotCon '95 into chaos.) With this move, TF:G2 somewhat suddenly disappeared, and in January 1996 the first BW toys hit store shelves.
Beast Wars was a huge hit, and when you include the followup Beast Machines, the "Beast Era" lasted for five and a half years, starting at Kenner and then moving back to Pawtucket in 2000. After the Beast Era, Hasbro began what staffers have compared to a "Final Fantasy" approach to Transformers, whereby every few years a new line will be released which has similar themes to previous incarnations, but also exists as an independant entity, and the franchise has been going strong since then. The first line in this post-Beast regime was Robots In Disguise, running from about July 2001 until June/July of 2002. Armada was next, with the first toys appearing at retail early in the summer of 2002. This was followed by Energon, which continues the story from Armada, and then Cybertron, also in the same "universe" as the last two, which began hitting stores in June 2005. Additionally in the early 2000s, sales of TFs were strong enough that Hasbro began offering side toylines such as Universe and Alternators.
Sometime around early 1983, Takara began selling some of their popular Japanese robot toylines in the United States, including marketing Diaclone under the name Diakron and parts of New Microman under the name Kronoform. Shortly afterwards, though, Takara and Hasbro representatives met at the annual Toy Fair trade show in New York. Takara was trying to find US-based partners to help them sell their brands, and struck a deal with Hasbro. The two companies already had some business history together, as described elsewhere in the FAQ. (See