Wikipedia
Micromasters is a Transformers subline composed of small figures that came packaged in groups and with bases that interacted with the figures. They were sold at the peak of Galoob's Micro Machines craze and were packaged in groups of four just like Micro Machines. The Micromaster Combiners sub-line was made with a similar gimmick to rival Matchbox's Connectables line.
In the fiction, the Micromasters were created by the Transformers in response to growing power needs; It was costly and inefficient to continue to create or repair existing Transformers in large bodies. Utilizing technology gained from the Nebulon "master" process, a smaller, more efficient form was constructed. Until this time, small Transformers were limited in intelligence or ability in some way, such as the cassette robots needing a symbiotic relationship with Blaster or Soundwave.
Some Transformers chose to do away with their old bodies and become smaller; The majority of those who remained looked down on the smaller Micromasters. Due to their young age, at the time of the Great War no Micromasters had officer status in either the Autobot or Decepticon army. By the time of the discovery of Zone Energy, Micromasters were beginning to move up the ranks. This foreshadows the smaller, more energy efficient bodies of the Maximals and Predacons in the Beast Wars TV show in comparison with the much larger bodies of the Generation One Transformers.
The name "Micromasters" was only invented during the second year (1989) of the subline. The toys released in the first year (late 1988; Off Road Patrol, Race Car Patrol and Air Strike Patrol) were labelled as "Micro Transformers".