Everett Marshall

Everett Marshall was an American Civil War soldier on the side of the Confederate States of America. He was present during the Battle of Gettysburg but, due to a malfunction caused by the Sixth Doctor's TARDIS, was flung forwards to the 1980s. There he became a state ward patient due to no one believing his story, under the watch of Doctor Carl Jenner. In 1986, another rift in the Time Vortex sucked Marshall and Dr. Jenner back to the year 1862, at which point Marshall attempted to use his knowledge of history to change the events of the war so that the Confederates would beat the Union Army. (NOTVALID: Doctor Who and the Rebel's Gamble)

Battle of Gettysburg
Marshall was a member of the 2nd Georgia Infantry Regiment at Gettysburg in 1863. He served with his brother, Frankie Marshall, and several of his close friends. However, during the actual battle, Everett was suddenly shifted through cracks between the Vortex Barriers, sending him forwards in time to the 1980s. (NOTVALID: Doctor Who and the Rebel's Gamble: "The Adventure")

Unbeknownst to Marshall, this was actually caused by a malfunction in the Sixth Doctor's TARDIS, which later arrived at Gettysburg among a specific series of possible events. (NOTVALID: Doctor Who and the Rebel's Gamble: "Player's Note", et. al)

Life in the future
In the 1980s, Marshall eventually was committed as a state ward patient. In 1986, he was given a new Psychiatrist named Doctor Carl Jenner. Jenner was himself a Civil War enthusiast and recreationist, and believed he could help Marshall. Marshall began to speak to Jenner of his survivor's guilt, and his belief that the other members of the 2nd Georgia Infantry were trying to pull him back. He reflected on his guilt of his brother Frankie, who records claimed died in the battle which he was taken from. Marshall continued to insist that he felt like something was pulling him back, just as another crack between the Vortex Barriers opened, sending both him and Jenner back to the year 1862. (NOTVALID: Doctor Who and the Rebel's Gamble: "The Adventure")

Changing history
Now in the past, Marshall intended to change history so that the South would win the Civil War. Part of his plan involved stopping the death of Stonewall Jackson so that the leader would still be able to advise Robert E. Lee on the battlefield. The Sixth Doctor soon arrived in the era with his companions, Peri Brown and Harry Sullivan. The Doctor found of Marshall's attempted alteration to history and set out to stop him.

By some possible outcomes, Marshall was indeed able to fully or partially change history, resulting in an alternate timeline where the Confederate Army won the war. (NOTVALID: Doctor Who and the Rebel's Gamble: "Outcome 1", "Outcome 2", "Outcome 3", "The South Wins") However, these possible timelines were ultimately unstable due to the paradox of the TARDIS never making it to the Battle of Gettysburg, thus never sending Marshall to the future in the first place. Thus, a Time loop was triggered until the Doctor was able to make it to Gettysburg. (NOTVALID: Doctor Who and the Rebel's Gamble: "Player's Note")

Battle of Gettysburg
In accounts where the Doctor did make it to Gettysburg, one possibility indicated that the Doctor himself died preventing history from being changed. While Gettsyburg played out as it should have, Marshall was still free to meddle with the rest of the war and Peri and Harry were stranded in the 19th Century. (NOTVALID: Doctor Who and the Rebel's Gamble: "Outcome 5")

In a final account, the Doctor was not only able to prevent Everett from changing the events of history, but also saved his brother Frankie from dying in the battle. Now together, the two brothers agreed to return to 1986 and live the rest of their lives in the 20th century. (NOTVALID: Doctor Who and the Rebel's Gamble: "Outcome 6")