The Lone Centurion

"The Lone Centurion", or occasionally "the Last Centurion, was an epithet applied to Rory Williams, (TV: The Big Bang, A Good Man Goes to War) who was affectionally nicknamed Rory the Roman by the Eleventh Doctor, (TV: The Impossible Astronaut) following his living through centuries of human history in the guise of an Auton Roman Centurion to protect Amy Pond in the Pandorica. (TV: The Big Bang)

Background
The Romans being Amy Pond's favourite topic at school, Rory Williams, a friend of hers since childhood dressed as a Roman centurion on at least one occasion. There, he posed for a photograph alongside Amy. (TV: The Pandorica Opens)

While traveling with Amy, then his fiance, and the Eleventh Doctor in the TARDIS, Rory Williams was fatally shot by Restac, and erased from time when his corpse was consumed by a nearby crack in time. (TV: Cold Blood)

The Lone Centurion
An Auton duplicate of Rory, created as part of the Alliance's plan to prevent the Doctor from destroying the universe, had been formed from psychic residue from Amy's home, including a children's book on Roman centurions and a photograph of Amy and Rory taken at a costume party where Rory had worn a Roman centurion costume. The Nestene Consciousness created a fake Roman army, and included the replicant of Rory Williams. It placed them near Stonehenge in the year 102 AD as part of an elaborate trap for the Doctor. While the Auton Roman soldiers believed they were, indeed, Romans, the Auton version of Rory retained the memories and personality of the real Rory. He initially dismissed his other life as a dream.

When news came to the Roman encampment of visitors, Auton Rory volunteered to help, which led him to encountering the Doctor and Amy. He saved Amy by destroying a Cyberman, though she was knocked unconscious. The Doctor initially did not react to him, then welcomed him back, though precisely how this (Auton) Rory still existed was a mystery to the Doctor who was not aware of his nature or origins as an Auton.

Auton Rory learned he had been erased from time and Amy's memory when she did not recognise him after she woke. Encouraged by the Doctor — who returned the engagement ring that Rory had given Amy — Auton Rory set out to make her remember him. While his efforts were successful, Amy's memories returned at the precise time as the Alliance's trap began to unravel upon the Doctor. Part of this sequence involved activating the Autons (including Rory) in order to bring them under Nestene control. He urged Amy to run, but she refused, hugging him as the Auton programming activated, opening his hand and shooting Amy, causing her to die. (TV: The Pandorica Opens)

Following the total event collapse, all the other Autons were erased, except for the duplicate Rory who was left on Earth, the only remaining planet, weeping over Amy. It was then that the Doctor suddenly appeared in front of him to tell him that Amy was not completely dead and swiftly ordered him to open the Pandorica with the sonic screwdriver for the purpose of rescuing the Doctor's earlier self. A bewildered Rory followed these instructions, which led to a reunion with the earlier bewildered Doctor. Because most of the universe had been erased and the Nestenes were now non-existent, Rory's mind was fully restored and he was now in unfettered control of his actions.

To save Amy, the Doctor placed her in the Pandorica, where her life would be restored, though she would be in there for nearly two thousand years to complete the process. The Doctor, using River Song's vortex manipulator, offered to take Rory to retrieve Amy in the future, but the duplicate Rory refused, saying he had to make sure no harm came to the Pandorica. The Doctor admired Rory's humanity, Auton or not, and left him to his duty. (TV: The Big Bang) At some point, Rory had farmers remove the Pandorica for a nobleman from the Roman town of Isca. (PROSE: The Constant Warrior)

Rory watched over Amy for nearly two thousand years, following the box wherever it went and became the stuff of legend as "the Last Centurion" — a mysterious figure dressed as a Roman soldier who stood guard over the Pandorica, warning off those who would attempt to open it, a mythical sentinel whose story appeared in the folk history of a dozen civilisations. (TV: The Big Bang)

During his time guarding the Pandorica, Rory assisted King Harold Godwinson in the Battle of Hastings during the Norman conquest of England, evidently as his top general, befriended Samuel Pepys, and saved the infant daughter of Pepys's baker during the Great Fire of London before he bade farewell to Pepys and travelled to the city. In the 19th century, Rory became the inspiration for political cartoonists, and, in 1934, h released many leaflets that showed himself and Adolf Hitler with the message; "DON'T LISTEN TO HITLER. HE'S RUBBISH." (PROSE: The Constant Warrior) During the London Blitz of 1941, Rory was spotted moving the Pandorica out of harm's way during a bombing, but after that the Last Centurion disappeared from history and was believed killed or destroyed.

By 1996, Rory was working as a security guard at the museum where the Pandorica was now kept. There, he was reunited with Amy, when the Pandorica was opened by a younger version of her, freeing the older Amy from the Pandorica. Rory informed the Doctor of his previous meeting in 102 AD, leading the Doctor to travel back in time to have his original encounter with Rory. Ultimately, the Doctor piloted the Pandorica into the heart of the exploding TARDIS, which restored the universe, but also rewrote much of its history. The Doctor was removed from reality, and with him gone, the Auton version of Rory was likewise removed from history. The original, human Rory was restored, his death having never occurred. (TV: The Big Bang)

Legacy
As the Doctor was remembered by Amy, he reappeared at her and Rory's wedding, at which point Rory remembered being "plastic". (TV: The Big Bang) On their honeymoon, Rory wore his Roman outfit while Amy assumed her kissogram police officer costume. (TV: A Christmas Carol)

While meeting a future version of the Eleventh Doctor in Utah, Rory was greeted as "Rory the Roman". (TV: The Impossible Astronaut) Rory confided in the present Doctor that he could remember the two thousand years he spent waiting for Amy as "the Last Centurion". However, he added that he did not remember it all the time, likening it to a door in his head which he could shut. (TV: Day of the Moon)

On the Doctor's idea, Rory later adopted the mantle of "the Last Centurion" again when it was revealed that the now pregnant Amy had been abducted. As a centurion, he faced the Cyber-Leader of the Twelfth Cyber Legion, which was destroyed by the Doctor, learning that Amy was at the space station, Demons Run. He then appeared at Stormcage Containment Facility to recruit River Song, who questioned his attire. Learning the Doctor chose it, River observed his rules of engagement "float like a butterfly, sting like a bee", to which Rory added "look ridiculous" while River jokingly suggested heels. However, River informed Rory that she could not participate in what she knew to be the Battle of Demons Run.

Meanwhile, at Demons Run, Amy told her baby daughter, who she named Melody Pond, of her father: "There's a man who's never going to let us down, and not even an army can get in the way. He's the last of his kind. He looks young, but he's lived for hundreds and hundreds of years. And wherever they take you, Melody, however scared you are, I promise you, you will never be alone. Because this man is your father. He has a name, but the people of our world know him better as the Last Centurion."

- Amy Pond

Eventually, Rory, armed with a sword, appeared at Demons Run, where he intercepted Madame Kovarian before she could depart the station with Melody, who he returned to Amy before shedding tears, to which Amy assured him "crying Roman with a baby, definitely cool." Though the Church forces were escorted off the station, the Headless Monks secretly remained aboard the station before revealing themselves. As the Headless Monks attacked, Rory fought alongside Strax, Vastra, Jenny Flint and Lorna Bucket, ultimately defeating all of them. (TV: A Good Man Goes to War)

In River Song's World, the Doctor recalled Rory's epithet as "the Last Centurion" while recalling the circumstances of his own death at Lake Silencio to Winston Churchill. (TV: The Wedding of River Song)