Optimus Prime is an ancient Cybertronian and one of the most significant surviving Autobots, carrying a history shaped by war, leadership, loss, and prolonged conflict. By the events of Transformers: Age of Extinction, he has already spent years fighting alongside the Autobots through the Cybertronian war and the battles that eventually brought the Transformers to Earth. His life has been defined by the survival of his people and by the responsibility of leading those who remained under his command. He is not simply another Autobot soldier. He is a Prime, a figure whose name carries authority among the Autobots and whose decisions have repeatedly placed him at the center of their struggle for survival. The events of the earlier war and the Battle of Chicago have left the Autobot population severely diminished, with Optimus continuing forward despite the loss of many of those who fought beside him.

After the Battle of Chicago, the relationship between humanity and the surviving Autobots deteriorates severely. The United States government terminates its cooperation with the Autobots, while the public increasingly regards Transformers as a threat. Although the Autobots are supposedly under protection, Cemetery Wind secretly begins hunting them. Optimus becomes one of their principal targets, while Lockdown pursues him on behalf of the Creators. The situation forces Optimus and the surviving Autobots into hiding rather than allowing them to operate openly as they had before. The pursuit becomes personal when Lockdown tracks down Ratchet. Ratchet refuses to reveal Optimus's location and is killed for protecting him. The loss adds another death to the long history of casualties surrounding Optimus and leaves the surviving Autobots increasingly isolated.

Optimus himself eventually suffers a devastating attack in Mexico City. He is badly damaged and forced to conceal himself in an abandoned vehicle form while trying to survive without the support of his team. He eventually ends up in Texas, where Cade Yeager discovers him and initially considers him little more than a valuable piece of alien technology. Cade nevertheless chooses to repair him rather than turn him over. Optimus remains physically damaged and vulnerable during this period, making his recovery dependent upon someone outside the Autobot ranks. Once he is capable of moving again, he does not remain hidden indefinitely. He reconnects with the surviving Autobots, including Bumblebee, Hound, Drift, and Crosshairs, and resumes his position among them.

The discovery of what has happened to the Autobots reveals the scale of the persecution against them. Optimus learns that surviving Autobots have been systematically hunted, killed, and collected, while their bodies and remains are being transferred to Kinetic Solutions Incorporated for technological research. Leadfoot is among those killed, and the footage of his death gives Optimus and the other Autobots direct evidence of what has happened to their kind. Their enemies are not limited to one faction. Cemetery Wind is hunting them on Earth, KSI is exploiting their remains, and Lockdown is pursuing Optimus for an entirely separate purpose connected to the Creators. Optimus therefore finds himself fighting for more than his own survival. He is carrying the remaining Autobots through a period in which their existence itself is being threatened.

The revelation surrounding the Creators expands Optimus's understanding of his own history. Lockdown tells him that the Creators built him and that they now want him returned. Optimus refuses to accept ownership or obedience on that basis, declaring that he is a slave to no one. Lockdown subsequently captures him and takes him aboard his ship, where Optimus is placed among the Knights and other rare Cybertronian specimens that Lockdown has collected over centuries. The encounter establishes that Optimus's existence reaches much further back than his experiences on Earth. He belongs to an ancient species whose origins are connected to beings who created the Transformers for purposes that remain only partially understood.

During his captivity, Optimus encounters the Dinobots, ancient Cybertronian warriors who have also been imprisoned by Lockdown. His imprisonment is temporary because Cade, Bumblebee, and the other Autobots infiltrate Lockdown's ship and free him. Optimus then takes control of the situation and seeks the Dinobots' assistance. Rather than treating them merely as weapons to be used, he confronts Grimlock directly and establishes his authority through combat before the Dinobots join the Autobots. Their release gives Optimus a powerful new force at a moment when the surviving Autobots are badly outnumbered and facing an increasingly dangerous enemy.

Optimus subsequently returns to Earth and leads the Autobots into the battle against Galvatron and KSI. The conflict is larger than the immediate survival of one group. KSI has developed artificial Transformers using Transformium and stolen Cybertronian technology, while Galvatron represents the return of Megatron in a new form. Optimus therefore confronts an enemy who carries the history of his oldest adversary while simultaneously facing a new generation of artificial machines created by humans. The battle ultimately takes place in Hong Kong, where Optimus and the Autobots fight to stop KSI's plans and prevent the Seed from being used in a way that could cause catastrophic destruction.

By the final battle, Optimus is fighting alongside the Autobots and the Dinobots as the last major defense against Galvatron's forces. After defeating the immediate threat, he does not simply settle into a peaceful return to Earth. He recognizes that the danger surrounding him has not disappeared. There remains a price on his head, and his continued presence places the people who helped him at risk. He therefore decides to leave Earth and take the Seed somewhere it cannot be found. His departure is voluntary and connected to his responsibility for protecting those around him. Before leaving, he entrusts Cade and the Autobots with the protection of the Yeager family and acknowledges the debt between them.

Optimus's final departure marks another stage in a life defined by movement, conflict, and responsibility. He leaves Earth knowing that the Creators remain a threat and that Lockdown's pursuit has revealed a larger history behind his existence. He carries the losses of the Autobots who were killed during the persecution, including Ratchet and Leadfoot, while the surviving Autobots remain scattered and changed by everything that has happened. His decision to leave also separates him from the human family that helped save his life, even though he leaves them with the protection of his remaining allies. His final words to Cade place their relationship within the larger history of his life, expressing gratitude while accepting that their paths may separate.

Optimus Prime's legacy by the end of Age of Extinction is therefore the legacy of a surviving Prime who has endured the collapse of Cybertronian society, years of war, the deaths of comrades, the destruction of his people, betrayal by former human allies, systematic hunting on Earth, physical defeat, captivity, and the discovery that the beings who created his species still seek control over him. Despite everything that has happened, he remains connected to the Autobots and continues carrying responsibility for their survival. His history on Earth becomes only one chapter of a much older existence. By leaving Earth to pursue the Creators, he moves toward the unresolved origins of his own kind while leaving behind the people and Autobots who became part of his life during the events surrounding Cade Yeager. His story at the end of the film remains unfinished, with his next objective being to find the Creators and demand answers for what has been done to him and his fellow Transformers.