In Assassin's Creed Syndicate, Jacob is the Frye twin who leads the London Assassins.
Jacob Frye and his twin sister Evie travel from Crawley to London in 1868, during the Industrial Revolution. Jacob is impulsive and focuses on organizing street gangs and confronting the Templars directly. Evie is more methodical and concentrates on recovering an Isu relic while supporting the broader campaign.
The two siblings share the protagonist role, but the question asks specifically which twin leads the London Assassins. Jacob establishes and commands the Rooks, a gang that becomes the Brotherhood's main street-level force in London. Evie remains a full playable protagonist rather than merely a supporting character.
The game's historical London includes figures such as Charles Darwin, Charles Dickens, and Queen Victoria. Assassin's Creed Syndicate was released in 2015 and is notable for its Victorian setting, horse-drawn carriages, grappling launcher, and paired protagonists.