Jacob Frye is the protagonist of Assassin's Creed Syndicate alongside his twin sister Evie.
Syndicate is set in London during the Industrial Revolution and follows the Frye twins as they challenge Templar control over the city. Jacob is more impulsive and openly confrontational, while Evie is generally portrayed as more focused on planning, stealth, and recovering Pieces of Eden.
Ubisoft Quebec developed the game, which was released in 2015. Its London includes districts and landmarks inspired by Victorian life, and the protagonists can use a rope launcher to traverse buildings more quickly. Jacob also leads the Rooks, a street gang that becomes an Assassin-aligned organization.
The question specifies Jacob because Evie is equally important and playable. Some summaries call the pair the protagonists of Syndicate, but the individual answer sought here is Jacob Frye. Henry Green, also known as the Indian Assassin, is a major ally rather than one of the Frye twins.