Megatron is (in most tellings of Transformers) the founder and leader of the Decepticons - look at any animated iteration of the franchise and most print ones, and it will be him at the villainous faction's helm. However, this is not always the case where Megatron is the one calling all the shots.
In many Transformers stories, particularly ones told through the comics, Megatron becomes indisposed at either the hands of the Autobots or one of his one treacherous underlings, leaving other Decepticons to take (or usurp) his place as leader. Here's a look at some Decepticons who've held the top dog position.
10 Shockwave Took The Lead After A Failure By Megatron
The first Decepticon to successfully take Megatron's place, the coldly logical Shockwave debuted in the Marvel-published Transformers comic at the end of issue #4, defeating the remaining Autobots after they'd felled his Decepticon brethren. From there, Shockwave set about repairing the other Decepticons while making it clear to Megatron that he was no longer calling the shots - if he'd already failed, then logically, it was time for someone else to take command.
Shockwave remained leader until issue #19, when he ceded command after a failure of his own. This demotion didn't last long - in issue #25, when an erratic Megatron seemingly destroyed himself, Shockwave stepped up as leader once again.
9 Starscream Was In Command After Megatron Was Critically Wounded
The Decepticons' Air Commander, Starscream's treachery is his defining trait - yet, to his own peril, he tends to be much less successful at overthrowing Megatron than his aforementioned cyclopean comrade. Still, there have been occasions when Starscream has gotten a shot at power, if only briefly. In the IDW comic continuity, after Megatron was critically wounded in All Hail Megatron, Starscream was left to lead in his place, but between an inability to organize the troops and the Decepticons' meager energy supplies post-withdrawal from Earth, the faction nearly fell apart under the Seeker's watch until Megatron returned.
Similarly, in Transformers Prime's opening episodes, Starscream is in command of the Decepticons from episodes 6-14 while Megatron slumbers in a stasis-lock coma, but the Decepticons don't respect him nor do the Autobots fear him; once Megatron returns, Starscream falls by his way side and stays there for the rest of the series.
8 Soundwave Became Leader After The Destruction Of Shockwave & Disappearance Of Galvatron
Usually the only one of Megatron's lieutenants without any plans to overthrow him, there have been occasions where Soundwave has stepped up. In UK-exclusive stories of the Marvel comic continuity, set in 2006 after the events of the animated movie, Soundwave stood up as leader following the destruction of Shockwave and disappearance of Galvatron. Allying with the Autobots to defeat a Quintesson invasion, Soundwave briefly pondered a more permanent truce before deciding the history between the two factions made that impossible.
Likewise, in the IDW continuity, after Megatron's change-of-spark and defection to the Autobots, Soundwave took control of the Decepticons (using Galvatron as a figurehead), intending to take them back to their roots as a group intent on equality for all Cybertronians, even establishing a space station colony in orbit of Jupiter for the Decepticons to call home.
7 Straxus Ruled While Megatron Lay Dormant On Earth
In the Marvel comic continuity, while Megatron lay dormant on Earth for millions of years, the warlord Straxus seized control of the Decepticon forces on Cybertron. Operating from his fortress Darkmount, Straxus was even more unhinged than his predecessor, melting both Autobot POWs and neutral Cybertronians in a smelting pool.
Though seemingly killed by the Autobot Blaster in issue #18, UK-exclusive stories revealed Straxus had survived, albeit reduced to an immobile head, and he had his consciousness transferred to a clone of the Decepticon whose leadership he had usurped - from there, he posed as Megatron until the genuine article confronted, and ultimately, destroyed him.
6 Ratbat Proved To Be An Effective Leader Until His Destruction In The Underbase Saga
Though just another of Soundwave's animalistic underlings in The Transformers cartoon, the Marvel comic portrayed Ratbat as the fully sentient fuel auditor of the Decepticons. A bureaucrat at heart, Ratbat was aghast at the wanton energy usage of the Earthbound Decepticons, eventually coming to Earth and taking command to ensure more efficient use of resources. Running a tight ship, Ratbat proved surprisingly effective as leader until, like many other characters, he was destroyed during the four-part "Underbase Saga" (issues #47-50).
5 Scorponok Led Decepticons Who Pursued Autobots In Command Of Fortress Maximus To Planet Nebulos
In the Marvel continuity, Scorponok led a group of Decepticons who pursued the Autobots in command of Fortress Maximus to planet Nebulos - Autobot and Decepticon alike "binary-bonded" either their heads or their weapons with several of the inhabitants, becoming Headmasters/Targetmasters.
After the Nebulos Autobots received a distress call from their Earthbound comrades, they left in pursuit of the message, bringing Scorponok's Decepticons with them. Upon arrival, Scorponok and his cons clashed with Ratbat's forces, until Scorponok personally deactivated the fuel auditor in issue #50. From there, he remained leader of the Decepticons for the bulk of the remaining run, even having something of a redemption when he allied with Optimus Prime to defeat Unicron then perished at the Chaos Bringer's hands.
4 Thunderwing Claimed The Matrix Of Leadership Which Eventually Consumed His Mind
When a power vacuum formed among the Cybertron-based Decepticons after the death of Straxus, the Pretender Thunderwing climbed the ranks and seized power with sheer displays of military might. Though an adept commander, it wasn't long before Thunderwing set his sights on claiming the Matrix of Leadership as his own, an obsession that slowly but surely alienated his followers.
Though Thunderwing eventually succeeded in claiming the talisman, it was a pyrrhic victory - his ownership of the Matrix tainted its very essence, and the corrupted Matrix consumed Thunderwing's mind, forcing the Autobots to destroy both the Decepticon and (seemingly) the Matrix itself. Thus, Thunderwing's leadership and existence met an ignominious end.
3 Bludgeon Was The Next Leader After The Fall Of Scorponok
After leading the Mayhem Attack Squad under Thunderwing, Bludgeon became leader of the Decepticons as a whole following the demise of Scorponok. Faced with the imminent destruction of Cybertron, Bludgeon severed the Autobot/Decepticon alliance that had (barely) defeated Unicron, preferring to maroon the Autobots on their dying homeworld while the Decepticons set out to begin a new conquest. Fortunately, those plans were foiled by a revived Optimus Prime.
Though Bludgeon only had five issues as leader before the Marvel comics' untimely cancellation, both of writer Simon Furman's (mutually-exclusive) follow-ups, Generation 2 and Regeneration One, gave the skull-faced Pretender more time to shine. Still, in both tales, Bludgeon's dream of leading an interstellar Decepticon empire were foiled by either a revenant Megatron (G2) or a newly-christened Rodimus Prime (RG1).
2 Overlord Seized Control Of A Prison & Ruled With Fear
Introduced in the Japanese-exclusive TV series Super-God Masterforce, Overlord was originally a non-sentient "Transtector" piloted by couple Giga & Mega, servants of the "Decepticon God" Devil Z. In the series finale, Overlord, along with the rest of the Transtectors, were granted sentience and fled Earth to continue their battle amongst the stars, making occasional cameos in sequel series Victory.
Reintroduced to western audiences in comic mini-series "The Last Stand Of The Wreckers," Overlord, here a standard Cybertronian-born Decepticon, seized control of Autobot prison Garrus-9 single-handily and transformed the complex into his own personal empire, ruling his Decepticon subjects through fear and forcing the Autobot guards-turned-captives into lethal gladiatorial matches.
1 Galvatron Led A Failed Attempt At Conquering Earth
Typically a reborn Megatron, the Galvatron of the IDW Transformers continuity was an exception. This Galvatron was a very different character than past iterations; a Transformer from Cybertron's primordial past whose existence long-predated the Decepticons' founder, Galvatron had been both a servant of the corrupt Nova Prime and twin brother to the future Autobot Arcee. Granted immortality by contact with the Dead Universe and made a servant of its sole inhabitant, D-Void, Galvatron was freed from its effects around the same time Megatron renounced the Decepticons.
Partnering with a despondent Soundwave to lead the Decepticons in a new direction, Galvatron's innate violence clashed with Soundwave's attempts at reforming their faction towards peace. Thus, the Decepticons splintered, Galvatron leading his followers in attempted conquest of Earth before being driven from the planet then slain by the combined forces of Optimus Prime, Soundwave, and Arcee.