These were detailed on the character bios that the toys came with, and later on in the cartoon and comic series which were created to act as advertising platforms to the toy-line. Some received new colors for the Western market, and various action features were also removed for safety reasons, but the most vital change was giving each figure a unique name, a personality, special abilities, and tying all the unrelated toy universes together into a single large mythology. Most of these 'Pre-Transformers' came from Takara's Diaclone (which were in fact released under the titles Diakron and Kronoform in the US, albeit with little success) and Micro Change lines.
What we regard as the Transformers brand today actually originated from multiple, often unrelated Japanese robot toy-lines - Hasbro, the distributors of Transformers merchandise in the Western world, imported various transformable action figures from the Japanese toy manufacturers Takara, Takatoku Toys, Toy Box and To圜o.
A few people seem to be confused over whether Transformers started as a toy or a cartoon (or comic) franchise, and even people officially affiliated with the franchise, such as the infamous comic artist Pat Lee, have gotten the answer wrong.