Transformers is a theme based on the transforming robots from Cybertron — the heroic Autobots and vile Decepticons — battling it out over the resources of Earth in hopes of defeating the other faction so they can save, or conquer, the universe. This particular theme is generalized Generation 1, reimaged in the designs used for the Universe/Classics sublines of figures, with a few alterations.
Gestalt and various alternate technologies exist but are in very limited use, many such group members exist as normal Transformers instead. Several G1 Micromasters are in a similar state, or as Minicons. The latter exist, but in much smaller numbers and are less of a threat to power balances, more often suited for the role of spies or maintenance aids than power boosters.
Both Primus and Unicron are regarded as god-like beings, but neither has yet to make an appearance, though a few 'heralds' of Unicron are rumored to be. But otherwise its the story of good vs evil you grew up with, with Robots in Disguise that are More Than Meets The Eye!