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Players were a group of the Immortals who tampered with history to amuse themselves.
They were capable of travelling through time, but their abilities were limited. They had knowledge of the Time Lords, and knew them to be devious.
They were originally the Mesopotamian Gods, but by the time they returned to Earth they had travelled through time so much and lived so long that they could no longer remember what they were or where they were from. (PROSE: Deadly Reunion)
One of the Players' more long-term plans was to eliminate Winston Churchill before World War II. However, their efforts to assassinate him in the Boer War were averted by the Sixth Doctor and Peri Brown, the Second Doctor saved Churchill from being captured and sent to Germany during World War I- the same effort resulting in Churchill being declared off-limits for some time as too much attention had been drawn to others' interest in him- and the Sixth Doctor and Peri again assisted Churchill in 1936 in preventing Edward VIII from dismissing the government in favour of a new parliament allied with Adolf Hitler. (PROSE: Players)
In an attempt to create new potential for more games, the Players attempted to arrange for Napoleon Bonaparte to win the Napoleonic Wars, the Countess having devised a plan to expand Napoleon's empire further and then allow it to collapse, his former subjects reverting to their original, smaller kingdoms and going to war with each other once again, allowing the Players to take control of the resulting small countries and direct their actions personally. These plans were thwarted by the Second Doctor, although his new companion Serena died in the process when she sacrificed herself to save the Duke of Wellington from an assassination attempt prior to the Battle of Waterloo. (PROSE: World Game)
Deciding that the time had come for an Endgame so that they could move on to other worlds, the Players attempted to start World War III in 1951 by plunging America and Russia into nuclear war; play would only end when one side annihilated the other. The Players used agents to influence the mind of Harry S. Truman in the White House, but were prevented when the Eighth Doctor informed the Secret Service of their plan.
In Russia, the Countess seduced Josef Stalin, and whispered in into his ear whilst he slept that China and America were aiming nuclear missiles at his cities. The Doctor convinced her to abort her game as she saw more potential to play further games on Earth, the Countess subsequently assisting him in stopping other Players' efforts to fully brainwash Truman. (PROSE: Endgame)