He has sometimes filled the role of Autobot leader and often butts heads with authority, most often with Optimus Prime.
Major Story Arcs
Grimlock and the Dinobots were amongst the Autobots who crashed on Earth 4 million years ago. They were repaired ahead of their comrades but wound up trapped in a tar-pit along with Shockwave, a Decepticon that they'd been sent to subdue. They were discovered by a probe sent by the recently-revived Auobots in the present but this also freed Shockwave who decimated their ranks.The Dinobots helped a survivor, Ratchet, to defeat Megatron and save their inoperative comrades. The Autobots were soon restored to full strength & the Dinobots joined their ranks.
Despite his aversion to others authority, Grimlock led the Autobots himself for two stints. While he had some successes, his leadership was often marred by rash decisions.
His first time as leader came in the wake of Optmius Prime's death where he saved the Autobots from a Decepticon attack, his valor impressing them that he might be a worthy leader. Under his command the Autobot's ship was repaired and their energy problems solved, but his totalitarian leadership style alienated many. He eventually learned to put his troops first and reconciled with a dissenter to save them from an ambush.
Optimus Prime was eventually revived and resumed leadership. Grimlock was rendered inoperative by a superpowered Decepticon's rampage, but was revived with Pretender technology, and joined the war effort on Cybertron. When Unicron, the planet-sized nemesis of the Transformers and their Creator-deity Primus was alerted to the planet's location Grimlock joined the quest to find the Matrix, an artifact thought capable of stopping him and able to revive fallen machines. When this fell though, Grimlock acquired and used an untested miracle substance called Nucleon to revive his fallen comrades.
Optimus Prime sacrificed himself to destroy Unicron, but nominated Grimlock as his successor before expiring. Grimlock saved the Autobots from a betrayal by the Decepticons, who they had allied with to face Unicron, but soon led them into a trap where most were destroyed. They were saved by a reborn Optimus Prime & the Last Autobot, a being with the bility to restore mechanical life, who was created by Primus to carry on His Will. The futility of facing enemies who could be endlessly revived caused the Decepticons to definitively surrender & go into exile, bringing the Transformers' war to an end.
Long before the war, Grimlock fought in the gladiatorial arenas on Kaon along with Stasrcream, Megatron, and others. When the war broke out, Grimlock ultimately sided with the Autobots. At one point in the war, Grimlock and other Autobots at Altihex are forced to retreat and this annoys Grimlock as this is all they have been doing and he claims the new Prime needs to be a strong military leader. Grimlock later meets with Prowl and Jazz at what was once the Helix Gardens to tell them that if the new Prime falters, they should take his title and power by show of force. When Optimus is receiving the matrix of leadership, he is attacked by a group of Decepticons and Grimlock does not allow the other Autobots to intervene because he wants to see how well Prime can handle them. However, after defeating the Decepticon ambush, Optimus declares a planet-wide evacuation of the planet and Grimlock feels that this move is a slap in the face to all who have died in the war to protect Cybertron. Grimlock later heads back to the old gladiatorial arena on Kaon where he is greeted by Starscream, Skywarp, and Thundercracker. Starscream tries to goad Grimlock into joining them and tells him of their plan to take out an Autobot command center at Sector Zero-six and that he can either warn them or help them pick off any survivors. Ultimately, Grimlock chose to warn the Autobots of their plan because even though he isn’t very fond of Optimus or most other Autobots, he hates Starscream and the other Decepticons more. Later, Grimlock and a group of Autobots are ordered by Prowl to go to the Forum of Enlightenment because Prowl believed it was connected to the Decepticons’ decision to attack Iacon. Deep within, they find one of Cybertron’s engine turbines but Grimlock leaves the others to go find Optimus Prime. As he searches for him, Optimus is eventually teleported near Grimlock and Grimlock tells him that he needs to stop just thinking and actually act. Prime says he does what he believes is best for all Transformers, but Grimlock says he’s not listening to them and that he didn’t come to rescue Prime, and that he will kill him if necessary. He then gives Prime his sword and tells him that if Megatron is a big problem, then he should kill him. Later, Prime returns and takes command of Grimlock’s troops and Grimlock asks him if he took care of Megatron, to which Prime says he did what had to be done. Later, after the planetary turbine is stopped, Grimlock talks with Optimus and Optimus says to him that he now understands what he goes through and that he spared Megatron to avoid giving into the dark legacy that Cybertron once was.
IDW Publishing Continuity
Long ago, Grimlock was a fighter in the illegal fighting circuit in the city of Kaon. Not much is really known other than that, though. He also has a grudge against the Decepticon Shockwave because he and the other Dinobots fought him long ago over control of an energon cache but when Shockwave realized he couldn't have it, he simply destroyed it and although he was told by Prime to just let it go, he never could. Later on, on Earth, some time after the ice age ended and the Earth began to warm up, Grimlock and the Dinobots had been observing Shockwave from their ship in orbit. While the other Dinobots were trying to figure out what Shockwave was doing, all Grimlock thought about was that he was alone and vulnerable and wanted to attack him. Grimlock demands they all go down there, but is told that the energon levels on the planet are too high and so to be able to land on Earth, they all take forms of (extinct) wildlife on Earth, with Grimlock taking the form of a t-rex and then before taking off, Grimlock targets a volcano with the ships weapons. Afterwards, the Dinobots all go down to Earth and attack Shockwave. But just as it seemed like they had won, Shockwave all of a sudden stops thinking logically and just begins to fight them in a rage-like state and ends up taking them down. Grimlock, unwilling to give in, gets up and transforms and heads for Shockwave but succumbs to the high levels of energon and is sent into stasis lock. Right afterwards however, the weapons from the Dinobots' ship fire upon the volcano causing it to erupt and Shockwave is covered in lava, along with the unconscious Dinobots, all of whom are still alive and preserved, but are in stasis lock.
Grimlock is often aggressive, brutish, stubborn and short-tempered. He hates weakness, and respects only the strong. And, since he sees himself stronger than most everyone else, he can be quite arrogant.
These traits, however, can be signs of his brighter traits; the fact that he never gives up a fight, is confident and quick to action. These traits make him a very strong warrior.
The fact that he is with the Autobotsmight be only because the only thing he hates more than weakness, is strength being abused. In other words, he hates bullies, and is not very fond of the Decepticons due to that.
In other incarnations, he tends to have little intelligence and is friendlier and more childlike than his usual brutal and intimidating self.
Powers and Abilities
Grimlock possesses immense physical strength, second only to Optimus Prime and Megatron. He has proven both skilled and physically strong enough to outbrawl the likes of Scorponok on multiple occasions. He is also nearly invulnerable to all kinds of physical damage, once surviving an explosion of a large refinery of energon at point blank range with seemingly little trauma. His great strength and durability makes him a formidable hand-to-hand combatant. In dinosaur mode his jaws are strong enough to snap in to virtually anything that comes between them. In robot mode, he has an energon-sword that can slice a 2-foot thick concrete wall with one sweep of it's crackling blade. In some incarnations, he is also a skilled and tactical aswell as an aggressive and brutal fighter. In other versions he is depicted as a dim-witted but powerful brute.
Transformers: Age of Extinction (2014) - Grimlock makes an appearance in Transformers: Age of Extinction. After Optimus Prime had freed him and the other Dinobots from Lockdown's ship, Grimlock fought Optimus anyway, but Grimlock quickly decided to work with Optimus and the Autobots. Grimlock and the other Dinobots then helped the Autobots defeat Galvatron forces, and helped Optimus reach Lockdown.
Transformers (1984) - He appears in the Transformers G1 cartoon, as one of Wheeljack's and Ratchet's creations. Wheeljack and Ratchet built him and gave him and the other Dinobots life because the Dinobots were going to help them defeat the Decepticons. Although he and the other Dinobots at first thought Grimlock would be the most fit to lead, and Megatron even manipulated them into trying to overthrow Optimus Prime. After this though, the Dinobots and Autobots were great friends, and continued to fight alongside each other for the rest of the series.
Transformers: Animated (2007) - He appears in Transformers Animated as the leader of the Dinobots and only member capable of speech (even though it's broken English). He and the other Dinobots Swoop (pterodactyl) and Snarl (triceratops) were created by Megatron as prototypes for his new body, but were captured by the Autobots and releases on a deserted island. they were always being used by other villains (primarily Black Arachnia). The Dinobots have a friendship with the Autobots, but are not close because of how destructive they can be. Grimlock is armed with a powerful fire sword capable of projecting powerful blasts of flame. Like the other two Dinobots, his T-rex 'dino-mode' can breathe fire.
Transformers: War for Cybertron (2010) - Grimlock along with Swoop appears in the Nintendo DS version of the game as a neutral character who is neither an Autobot or a Decepitcon. Optimus Prime remembered that Grimlock was one of the strongest warriors in Iacon and asked him and Swoop to join though they declined. Grimlock noticed how Megatron became stronger through use of Dark Energon and changed his mind though. During negotiations Swoop was captured and Grimlock asked Optimus to mount a rescue. After Swoop was rescued Grimlock joined the Autobots in order to protect Swoop. He participated in the battle against Trypticon and was one of the Autobots who stayed behind with Optimua on Cybertron.
Transformers: Fall of Cybertron (2012) -
Grimlock appears as one of the main characters in all ports of the game and is voiced by Greg Berger who voiced him in the original animated series. Grimlock was one of the many Autobots assigned to protect the Ark from the Decepticons though left his post along with his team the Lightning Strike and this offered an opening for the Deceptiocons to almost destroy the Ark. Optimus Prime enlisted Cliffjumper and Jazz to track Grimlock's movements through the Sea of Rust on Cybertron. Jazz and Cliffjumper found ruins of ancient Cybertronians where Shockwave was performing experiments with Inceticons and a tower capable of creating a Space Bridge, as well as evidence that Grimlock, Swoop, Snarl, and Slug had been captured. Sludge was damage to the point of status lock. Grimlock is later seen in Shockwave's lab where he was transformed into a Dinobot as part of an experiment. Grimlock had most of his intellect removed in order to increase his strength and combative prowess. Grimlock was held by a containment field but was able free himself while the disgraced Starscream was bidding his loyalty for freedom. Grimlock then went on a rampage throughout Shockwave's lab freeing Swoop, then Snarl, and finally Slug while defeating the Insecticon leaders Hardshell, Kickback, and Sharpshot. Grimlock then forced his way to Shockwave who was working on a replica of the Space Bridge Tower and defeated him by chewing off his arm and sent him flying with a tail thrust. Grimlock then destroyed the Space Bridge Tower setting the portal it created into an unstable decay. Grimlock and the Dinobots stayed on cybertron to fight Shockwave and the remaining Insecticons. Grimlock's parts are also available as a DLC for the Titan class in Multiplayer mode, and his parts are called "Berserker" while his armor set has his normal name, Grimlock.
Transformers: Rise of the Dark Spark (2014) -
Grimlock appears as a playable character in Rise of the Dark Spark. The Cybertron-part of the campaign takes place after War for Cybertron (the PS3, Xbox 360 and PC version) and the Earth part takes place in a different Universe (the movie Universe). Grimlock appears only in the Earth part, in chapter 12, where he saves Bumblebee and Drift from Lockdown and his forces. Grimlock appears again in the chapter after that, helping Optimus Prime, Bumblebee and Drift defeat the rest of Lockdown's forces in the city and helps Optimus reach Lockdown. His incarnation from the Cybertron-games appears in the Escalation mode.