Jacob Frye is one of the playable Assassin siblings and leads the central gang-building campaign in Assassin's Creed Syndicate.
Set in London in 1868, Syndicate follows twins Jacob and Evie Frye as they challenge Templar control during the Industrial Revolution. Jacob is more aggressive and focuses on recruiting allies and taking territory through the Rooks, while Evie places greater emphasis on stealth, investigation, and finding an Isu artifact.
Jacob's campaign missions commonly involve disrupting Templar influence across London's boroughs. Evie remains equally important to the main story and is playable throughout the game, so the question distinguishes Jacob's leading role from the broader partnership between the twins.
Henry Green, also known as the Assassin leader in London, is an ally rather than one of the Frye siblings. Jack the Ripper appears in downloadable story content, but he is an antagonist, not a playable Frye twin.