In Assassin's Creed Syndicate, Jacob Frye becomes the first playable character. The game opens with Jacob infiltrating a Templar-controlled factory in London in 1868, establishing the industrial setting and the conflict that drives the campaign.
Jacob and his twin sister, Evie Frye, travel from Crawley to London to challenge the Templars' control of the city. Their personalities and methods differ: Jacob favors direct action and builds the Rooks gang, while Evie places greater emphasis on stealth, investigation, and finding the Piece of Eden linked to the London Templars.
Evie is also playable throughout much of Syndicate, so the question is about the campaign's opening character rather than the only protagonist. London is the principal setting, and the story includes historical figures such as Alexander Graham Bell, Charles Darwin, and Queen Victoria.