He has sometimes filled the role of Autobot leader and often butts-heads with authority, most often with Optimus Prime.
Major Story Arcs
Grimlock was a member of the ark crew who was, along with 4 others, repaired and rebuilt with a dinosaur form then sent after Shockwave by the ship's computer after it detected the Decepticon wandering the Earth's Savage Land. Despite outnumbering their opponent 5 to 1, the battle proved difficult, and ended with all 6 combatants trapped in a tar pit for millions of years.
In the 1980s, the other Autobots on Earth were decimated when an Autobot probe accidentally awakened Shockwave, however it also alerted Ratchet, the last Autobot left active, to the Dinobots' location and he soon revived them. They were then pitted against Megatron, who guarded the deactivated Autobots bodies, but were quickly defeated, and the former Decepticon leader was instead subdued when Ratchet tackled him over a cliff-edge. Afterwards Ratchet revived the Autobots and the Dinobots were absorbed into their ranks.
Although he took the Dinobots and seceding from the Autobots for a time over dissatisfication with Optimus Prime's leadership, Grimlock later came to lead the Autobots himself following Prime's death. Despite getting off to a bad start by arrogantly nominating himself leader, Grimlock later impressed the Autobots by saving them from a Decepticon assault, as they thought this demonstrated the valor, selflessness and compassion that a leader required.
Under Grimlock's leadership the Ark was rendered operational and, and Wheeljack developed a device that met the Autobots' energy needs, however his ruthless approach in dealing with Earth populace upset his troops and caused two, Blaster and Goldbug to desert from their ranks. Their capture was made a high priority and Blaster eventually surrendered when Grimlock used human hostages against him.
Grimlock was also unwilling to share power when he came into contact with another faction of Autobots led by Fortress Maximus and so challenged him to a duel for leadership. Too badly damaged to fight himself, Maximus nominated Blaster to fight in his stead. During the duel, the Autobots were ambushed by the Decepticons, so Grimlock and Blaster put aside their differences to aid their comrades and drive the Decepticons back.
Optimus Prime was soon revived thanks to Maximus' orders and he subsequently resumed leadership of the Autobots, with Grimlock and Maximus appointed as lieutenants.
Grimlock later spent some time inoperative when Starscream used the power of the Underbase to decimate huge swathes of the Autobot and Decepticon ranks. He was later revived as a Pretender, once again by Ratchet but without the other Dinobots, whose absence he sharply felt. After a mission to retrieve the Matrix fell through, Grimlock broke from the Autobot ranks and acquired a mysterious substance called Nucleon then used it to revive the fallen Autobots, including the Dinobots.
He then returned to Cybertron with the revived Autobots and led them into battle with Unicron, who had laid siege to their homeworld. Optimus Prime destroyed Unicron using the Matrix, but was left fatally wounded and so chose Grimlock to succeed him as he passed on.
An alliance had been formed by the Autobots and Decepticons in the face of the threat that Unicron presented, but the Decepticons only maintained this long enough to betray the Autobots and strand them on Cybertron as it tore itself apart. Grimlock had forseen this however, and secured ships to replace the ones that the Decepticons had sabotaged, and also planted a tracking device on the Decepticon's ships.
Unfortunately, this was as far as his foresight went, and he recklessly led the Autobots into a trap which the Decepticons had set when they found the tracker. Only a handful of Autobots, including Grimlock survived the ambush. They were ultimately saved however, by a revived Optimus Prime, as well as legendary entity known as the Last Autobot. This being had been created by the Transformers' God Primus in the event of his death, to carry on his will. The Last Autobot restored the fallen Autobots, and the Decepticons, seeing the futility of a battle where their enemies were constantly revived, retreated and went into exile.
With Cybertron likewise restored by the last Autobot, Grimlock and the other Autobots returned to their homeworld to live in peace.
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.
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 - 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 - 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.