|“||My strategy is brrrilliant!||„|
|~ Onslaught expressing angry pride.|
Onslaught and the rest of his Combaticon squad are a group of former Decepticon political prisoners whose original bodies were destroyed. Starscream retrieved their sparks from prison storage and implanted them in derelict vehicles from Guadalcanal.
Through unknown means and for unknown reasons, Onslaught, the Combaticons and several other bots were all taken prisoner by Megatron, with their original bodies being destroyed and their sparks being put into storage.
Starscream, in an attempt to take control of the Decepticons with his own troop, broke into the prison storage and took the components necessary for five Combaticons, destroying the storage room afterward. He then placed the Combaticons' sparks into five different derelict vehicles from the Battle for Guadalcanal during World War II. Brawl Swindle, Blast Off and Vortex were placed into various land and air vehicles, while Onslaught was placed in a troop transport truck. All of the Combaticons then reformatted to form a tank, jeep, rocket pod, helicopter and missile carrier, respectively, with Onslaught being the biggest. Starscream anticipated that the Combaticons would attempt to betray him, so he left out reformatting their energy absorbers and told the Combaticons that only he could install them.
Onslaught agreed to have the Combaticons serve Starscream, emphasizing that the arrangement would be temporary. The six then captured several Autobots and Decepticons whom to steal energy absorbers from. Angry that his troops had been captured, Megatron ordered an attack on Starscream with Devastator as his ace, but the Combaticons form their own combiner, Bruticus and overpower the other Decepticons. However, just as they claim victory over Megatron, the Stunticons show up by forming Menasor and sucker-punching Bruticus. Megatron then exiles Starscream and the Combaticons to an asteroid, where the six bicker amongst each other until Starscream leaves.
Despite Onslaught advising against leaving the asteroid, Starscream leaves in a huff, and Onslaught decides to stop caring about him after an off-handed insult. The Combaticons manage to make their way to Cybertron using Blast Off as a tether and confront Shockwave. They then defeated him and his sentinels, taking control of the Decepticon HQ on Cybertron. In order to take revenge on the Autobots and Decepticons, Onslaught hacked the Decepticon space bridge and attempted to alter its polarity using his turret as a controller, thus causing the Earth space bridge to pull the planet toward the sun. The Autobots and Decepticons decided to confront the Combaticons on Cybertron, with Starscream explaining that Bruticus' weak spot is on his back, which Optimus Prime uses to down him. Megatron and Starscream managed to put on a ruse and fake Bruticus' destruction with a hologram, and Starscream was ordered to reprogram Bruticus to be loyal to Megatron in return for being accepted back into the Decepticon ranks.
Onslaught is a leader-class Decepticon, being 50% taller than the rest of the Combaticons in order to serve as the torso for their Combiner form Bruticus. He is typically navy blue with purple and moss-green accents, with fluctuating amounts of black and silver on his guns, joints, etc. His visor is either red or orange, depending on continuity, and his speech synthesizer is covered by a mask.
Onslaught transforms into an 8-10 wheeled missile carrier with a rotating detachable turret. When in robot mode, this turret attaches itself to his back and the wheels from his vehicle mode are attached to the backs of his limbs.
In the G1 Transformers cartoon, he speaks with a faux British accent. This accent is completely dropped in his Aligned incarnation.
As the leader of the Combaticons, at worst he usually commands the minimal amount of respect necessary to merge with them to form Bruticus of their own volition. Besides Swindle, the other Combaticons respect him enough to compliment him out loud and follow his orders without question.
Onslaught takes his leadership role very seriously, to an exploitative extent. He will usually stand back and allow the other Combaticons to handle the close-quarters combat while shooting at his enemies from a distance in his vehicle mode. This reluctance to get his hands dirty has resulted in him being tackled and knocked over while in his truck form multiple times. Only when all of Onslaught's current plans are exhausted does he result to close-quarters combat, which has garnered the negative reputation of other Decepticons thinking he is bloodthirsty. While taking pride in his strategic mind, he talks about himself more often than other Decepticons and comes off as somewhat vain.