The Master Spy (died 1916) was a Sage and member of the Templar Order that operated in London during World War I. There, he ran a spy network on behalf of the German government while also establishing a localized cult in service of the Isu Juno.
Little is known about the Master Spy's early life as a reincarnation of Juno's husband Aita or of his experiences as Aita's memories began conflicting with his own. By adulthood, whatever original personality he had was completely supplanted by Aita's, leading him to ferverently search for an unnamed "Beloved".
By 1916, both Winston Churchill and the British Assassin Lydia Frye had caught wind of the Master Spy's operations and teamed up to shut them down. Supplied with intel by Churchill, Lydia was able to eliminate many of the spymaster's followers and steal the sensitive information they had procured.
Lydia eventually tracked down and confronted the Master Spy at his hideout; a struggle ensued, but the Spy Master used a stun grenade to disorient the Assassin, giving him an opportunity to slip away. The Master Spy then made his way towards another stronghold, where a fight broke out between his followers and Churchill's men.
Undeterred, he and a small number of spies set to burning all documents containing evidence of Juno's existence. However, Lydia then reappeared and killed the followers, before assassinating the Master Spy himself, thereby eliminating the cult's presence in London.
In 2015, a Helix initiate relived Lydia's memories, which allowed Juno, whose consciousness entered a digital afterlife called the Grey following her release from the Grand Temple, to find out the Master Spy's fate so that "his pattern [could] be added to [her] own".
- Assassin's Creed: Syndicate (first appearance)
- Assassin's Creed: Uprising (mentioned only) 
- Assassin's Creed: Syndicate – The Master Spy
- Assassin's Creed: Syndicate – The Darkest Hour
- Assassin's Creed: Syndicate – The Apothecary Twins
- Assassin's Creed: Syndicate – The Magpie
- Assassin's Creed: Syndicate – Hopton's
- Assassin's Creed: Syndicate – Clarence Stock House
- Assassin's Creed: Syndicate – 17 Walpole Lane
- Assassin's Creed III – Modern day