The Dinobots are a group of five Transformers, part of the Autobot faction. Their exact origins and abilities vary from one version of Transformers to the next, but they are always exceptionally powerful Autobots, able to sustain heavy abuse and wield heavy firepower against their foes. In all media, they are depicted as being fiercely independent and liable to break away from the main group of Autobots when the mood takes them.
Due to their unique alternative modes, their memorable personalities and their fighting prowess, they are fan favorites in their cartoon, comic book and toy incarnations.
The creation of the Dinobots was almost happenstance. One particular day at Autobot Headquarters, the Autobots detected unusual seismic activity from within the walls of the cave. Ironhide investigated the disturbance and found the fossilized bones of dinosaurs. After researching more dinosaurs, Wheeljack made the suggestion that, because of their brute force and power, dinosaurs working for the Autobots would shake up the Decepticons. Ratchet agreed, suggesting robotic forms and Optimus Prime authorized the project.
Shortly after, Grimlock, Slag, and Sludge were created and unveiled, but during the presentation, the Dinobots went awry due to their lack of intelligence. They began to ransack Autobot Headquarters, inflicting major damage to Teletraan I. Wheeljack managed to subdue the Dinobots with his shoulder-mounted magnetic inducer. The Dinobots were deactivated and stored in the cavern where they were constructed. Later, when many of the Autobots were in peril, the Dinobots were given cerebral upgrades increasing their intelligence, but only to the point of possessing broken language, and rudimentary logic. This did not make them "civilized", but the upgrade allowed them to follow instructions and be sent into combat.
The Dinobots performed admirably in combat, saving the Autobots, forcing the Decepticons into retreat, and earning a permanent place in the Autobot ranks. They proved very useful when Megatron brought Cybertron into Earth's orbit through the Decepticon Space Bridge. Dismayed by his losses to the Dinobots, Megatron discovered and briefly exploited weaknesses that turned the Dinobots against the Autobots. To counter this, two new Dinobots were created - Snarl and Swoop. Grimlock reconsidered his betrayal after being saved by Optimus Prime from an exploding meteorite.
They are often brought in to face the largest threats. They have tangled with Devastator numerous times, defeated or stalemated Megatron (Grimlock was often able to battle him on his own), and even survived an assault against Unicron.
In the comic version, the Dinobots are quite different from their cartoon equivalents. They were not created on Earth, but are in fact Cybertronian Autobots. The Dinobots are something like an Autobot elite special ops team, under Grimlock’s direct command. It is made quite clear that the Dinobots’ first loyalty is to each other over their fellow Autobots.
During the series, not much is said about the Dinobots’ time on Cybertron. Most of what is learned comes as hints or references in dialogues. We learn Swoop has a grudge against the Decepticon Divebomb, caused by a number of defeats the Dinobot suffered to the Decepticon in fights over the name 'Divebomb', Swoop's original moniker. We also learn Grimlock and the Dinobots were as powerful and rebellious on Cybertron as they are on Earth, going so far as launching successful raids against the Decepticon forces without the knowledge of the Autobot leaders. In one such raid, the Dinobots stole a number of Decepticon spaceships and hid them away so well they were still intact when the Autobots returned to Cybertron 5 million years later.
The Dinobots were aboard the Ark with the other Autobots when they originally crashed on Earth. However, soon after the crash, Shockwave landed on Earth in search of the Ark, and the ship’s computer (A.U.N.T.I.E.) reactivated the Dinobots.
This would be all the US comics would see of the Dinobots for some time, but in the UK comics, Ratchet led the Dinobots back to the Ark, only to encounter a deranged Guardian robot. They beat him, but lose Swoop in the process, prompting the Dinobots to walk out.