Brains is a little former Decepticon and Wheelie's pal who came to Earth as Sam Witwicky's roommate in Carly Spencer's apartment. Both Wheelie and Brains got seperated from the Autobots and stowed in a Decepticon ship and rip the heart of the ship and thought to be perished. Five years later, he was imprisoned by KSI to download the severed heads of Decepticons including Megatron who was upgraded by humans into Galvatron.
Dark of the Moon (2011)
Both Brains and Wheelie went to the place where both Sam and Carly are living. Wheelie and Brains are shown to have a deep friendship by their partnership and their agreement on the final girl who becomes a mean one, but he was a total pervert going through Carly's underwear drawer and watching both Sam and Carly a kiss. He was not exactly happy with the livelihood arrangements to complain that Carly was treating them to be either toys or pets rather than the advanced alien refugees he claimed.
The mechanical duo went with their fellow housemates to the NEST's base of operations to give the Autobots an important information, but their supportive offer was refused by the complement scientist, Charlotte Mearing. During the meeting with her, Brains found himself tied to the vehicle form of Wheelie and his attempts to make bond with her, received him the threat of the military gunfire. Later, he involved the research with Sam, Agent Simmons, Dutch and discovered that two Russian cosmonauts were all hiding after a cancelled cosmic operation to the Moon. However, if the Autobots forcefully leave Earth by the human authorities, he and Wheelie were captured and shoved inside a cage. They begged for help from Sam, warning him the whole thing was a trap as a Decepticon. Both of these robotic dudes, along with the fellow Autobots, were presumed to be dead when Starscream destroyed the Xantium shortly after a brief launch.
Both Brains and Wheelie appreciated that they hopefully survived alongside the Autobots by one of the secret booster rockets, and came to the heroic support of Sam, Epps and the rest of humanity in Chicago, Illinois. He declared to them that no one was gonna exile the Autobots and soon marched off to battle, using the ride of Leadfoot into the city. However, they were left behind by the destructive Wreckers when they distracted Shockwave, having fallen while they were firing off.
As both Brains and Wheelie hopelessly embarked their adventure through the streets, mumbling about the lack of assistance, they happened upon a massively destroyed Decepticon ship. They rode it up to one of the Decepticon motherships hovering over the city of Chicago that was controlling several smaller ships like the variant they hijacked. They sabotaged and overrode the controls, dropping several of the small space fighters onto the battlefield, causing a distraction just at the right second for Soundwave, stopping Bumblebee from being destroyed after Wheeljack. In addition, this allowed the Autobots to gain an essential lead in battle, proving theire worth in the end as the giant Decepticon ship crashed into a large area of water.
Age of Extinction (2014)
When Brains is still alive for his survival from the aftermath of the battle in Chicago, he found himself captured and forcefully went to the slavery by both Joshua Joyce and Kinetic Solutions Incorporated (KSI). He currently sported a temporary substitute crutch made of his junked neck and a neck brace. He was put to the usual duty to help KSI engineers their own transformable robots, doing mental autopsy on the fallen Decepticons brought back to life from Chicago. It was he who created the discovery that the Decepticon leader Megatron lived and was using KSI to build him a new body under the name Galvatron. But Brains searched his captors that unwillingly listen to him though, as they tortured him whenever he wanted, not exactly giving him an encouragement to warn him. While Joshua was revealing the full extent of KSI's work with the element Transformium to Darcy Tirrel, he attempted to show the nature of KSI's atrocities to her. However, all he earned was the electrocution from Joshua.
The predicament of Brains finally came to an end if the Autobots raided the chief headquarters of KSI to avenge the slain member of the Autobots, Ratchet. He was thankfully liberated by Hound and was pleased to see Joshua Joyce quite by the Autobots, but Joshua informed Optimus Prime, the Autobot leader, that they technologically advanced the Transformers, demoralizing him, who called to have a retreat. Brains was more than disappointed, as he was looking on forward to taking retribution on his former captors. He later rejoined forces with the Autobots and their alliance of humanity at a train yard following their rescue of Optimus Prime from Lockdown's ship. He then shared the truth about how the Decepticon leader and his quest took down KSI. Tessa Yeager asked why he never told Joshua about Galvatron and he imitated humankind for absolutely causing their extinction with a little bit care for the situation. So he left to happily sniff the flowers and enjoy his new freedom.