Robots in the disguise of robotic dinosaurs
One of many types of Transformers. Namely, the Dinobots are a sub-type of the larger group of Autobots. Unlike most other Autobots, however, their transformed state is not that of a vehicle, but a robotic dinosaur. They were originally built by Wheeljack (also responsible for the Aerialbots) after his suggestion that the brute strength of the dinosaur form could prove to be beneficial to the Autobots. The original three Dinobots were Grimlock, Slag and Sludge. Grimlock was modeled as a Tyrannosaurus, Slag as a Triceratops and Sludge as an Apatosaurus. Initially the dinobots had very little intelligence and due to this caused serious damage to Teletraan I, the beloved onboard computer of the Ark. They were then subdued and deactivated by Wheeljack, who stored them in the cavern they were built (which also happened to contain the three skeletons used in their design). They were subsequently given cerebral upgrades so that they could understand commands and were then sent into battle against Decepticon troops. They, of course, fought admirably and were the main factor in the Decepticon defeat that day. It must be said, however, that Megatron was temporarily disabled while the battle occured, and the Decepticon forces were disorganized and leaderless.
It also must be noted that not all sources agree with their origin story as I have put it. Other sources demand that the Dinobots were Cybertronians originally, and it was the Ark's computer who reactivated them and gave them dinosaur shapes in order to fight Shockwave. However they came about, it is certain that they were given the shapes of dinosaurs once on Earth and were battle-tested and shown to be apt. They were much like an elite force within the the Autobots command structure, beholden more to themselves (Dinobot solidarity) rather than any larger faction. Soon after their battle with the Decipticons, Megatron convinced the three dinos to join with him. To combat this, Optimus Prime had two more Dinobots produced: Swoop, a Pteranodon and Snarl, a Stegosaurus. With these two bots, Prime engaged the other three in battle, and were actually defeated by the original three. This was known as the "War of the Dinobots." Prime, however, later saved Grimlock from an exploding meteorite and this caused Grimlock to join up again with him. All five Dinobots were reunited and could not be seperated after that. Grimlock is their de facto leader, as he is King of the Dinobots, and often reminds people of that fact. So noble does Grimlock believe his station that he had tried to wrest control of the Autobots from Optimus, only to later learn he error of his ways. Optimus Prime seems to carry infinite patience with the Dinobots, as their contributions are always worth any drama they stir up or stuff they happen to break.
Some time after this reunion it occured that the Ark was attacked by Constructicons while the Dinobots happened to be the only ones guarding it, who easily defeated the invaders. Only when Devastator was engaged could the Constructicons mount a serious force against them and even then the battle resulted in a stand-still. Once, during a later battle, the Devastator was used as the principle assailant on Autobot City's main weapons. Optimus, recognizing their experience and talent with dealing with Devastator, sent the Dinobots out to stop it. All of the Dinos suffered damage (save Snarl, who was not present) but managed to keep Devastator at bay.
At one time the Dinobots trained and lived on an island discovered by Powerglide which contained living prehistoric life. Decepticons, however, arrived on the island to collect energy and as you might imagine, battle took place. Showing much poetic justice, the Dinobots were pushed into tar pits during the fight. Fortunatly, Slag was able to burn the tar around them and thus allow for escape. Due to this near-fatal situation, it was deemed that Dinobot Island was too dangerous for them to live on, and is now presumed to be fly-by country. During the Cybertronium crisis, the Dinobots were asked to steal Cybertronium from the Decepticons. Grimlock refused, due to having been very recently almost destroyed by the Decepticons. None of the Dinobots were eager or prepared to face them again. The Dinobots fled to Cybertron where they were subsequently captured and forced to work as slaves mining Cybertronium. Only Swoop evaded capture by Shockwave's forces and was able to free the other Dinobots with the help of Spike and Carly. They returned to Autobot headquarters, with a fair bit of pirated Cybertronium, and were welcomed with open arms.
While the Dinobots are lucky in battle, conflict seems to follow them where ever they go. For instance, they once crash-landed on Quintessa, where they battled and defeated the Sharkticons (curiously, Snarl was not present for this either), and thus rescued Kup and Hot Rod from certain peril. Wheelie met up with them and took them to rendezvous with the other Autobots. Much has been said of Snarl's inexplicable absence during this time, and although it is not fully known I believe he was recovering from some battle-wound. I feel compelled here to breach the subject of the Dinobot's intelligence. While they may lack the sophistication of scholarly education and may get themselves into sticky situations, they are geniuses of warfare and subterfuge. The Dinobots can always be counted on to fight intelligently and competently. Was it not Grimlock himself who created the Technobots? Of course, his super-intelligence has been granted via an accident within Unicron's head. Indeed, with a vast display of wisdom, he later gave up that intelligence so that Computron could possess that power. No, the Dinobots are not dumb or stupid or even simple-minded. They are primitive, and have a primitive cunning to them. They, as some might say, know when to hold them and when to fold them. It is this instinct and talent for survival that allowed them to be among the very few to survive the Last Great War and see the Second Golden Age of Cybertron.
There has been much discussion in recent days as to the purportedly ancient origins of the Dinobots. The main evidence is the existance of an ancient group of Autobots named Dynabots, which fought in The War Within. A Grimlock was the leader of a team of Autobots known as the Dynabots. While to many this is conclusive proof that the Dynabots were ancient forms of Dinobots who fought alongside Sentinel Prime, it must be noted that robot and robot group names are often reused within the Transformers Universe, and they do not necessarily represent incarnations of the same spark. It is highly likely, however, that the Dinobots are a very old group of Autobots who have been battling the Decepticons for a long, long time.
Alternate Forms and Storylines
The Dinobots are also present within the Beast Wars, Beast Machines and Armada continuums. In Beast Wars, there is a Maximal named Dinobot (who was originally a Predacon), and Grimlock is also recreated as a Maximal. In Beast Wars Neo, the Dinobots are a group of Dinosaur-formed group of Predacons on Cybertron that follow Magmatron, a Gigantosaurus.
Beast Machines brought a rather large pantheon of Dinobots, with Magmatron continuing on as their leader. This group features Air Raptor - an Archaeopteryx, Dinotron - a Pachycephalosaurus, Striker - a Stegosaurus, Terranotron (Swoop), Triceradon - a Triceratops, and T-Wrecks - whose form I think you can take a guess at. Grimlock is nowhere to be found.
Within Armada, Grimlock returns as the leader in the form of a Velociraptor. Sludge is a Dimetrodon, and Swoop again goes by the name Terranotron. There is also Slapper, an Ankylosaurus and Triceradon is present as well.
The Dinobots have always been one of the top selling Transformers figures ever since they were first released in 1985. This is due to a number of reasons. One, the Dinobots have loveable and fun personalities. Two, they can stand-in as two toys - robots and dinosaurs. While it is true all Transformers can stand-in for two different toys dinosaur toys draws in a different crowd than trucks and cars. And even if one had a full complement of regular dinosaurs, the Dinobots were robotic dinosaurs, and thus infinitely worthy of addition. Think of all the biotic vs. robotic dinosaur wars that could be reenacted! So of course the toys sold like hotcakes. The primordial dino-form hits a nerve in our lizard brains, and is extremely desirable to the child mind. Sleek metalization only adds to it's cachet.
It is my belief that, like in the stories, the Dinobots will outlive most of the other Transformers, as their archetypal presence within the Transformers Universe ensures that they will always remain fan favorites. They, to me, represent more than the dull-witted dino-slaves portrayed in comics - they are the interesection of robotics and monstrosity fasioned in a timeless way; as hulking prehistoric beasts and smooth sentient machines from the far-away future. They are a juxtaposition within themselves, they are a fanciful dichotomy that fills the childhood need for dinotopic wonder.
Transformers Online Encyclopedia - http://www.geocities.com/Area51/Station/6563/dinobot.html
Bens World of Transformers - http://www.bwtf.com/dinobots/
Wikipedia's Dinobots entry - http://en.wikipedia.org/wiki/Dinobot_%28Generation_One%29