The main cast members of Slow Horses include:
- Gary Oldman as Jackson Lamb, the head of Slough House, known for his sharp wit and loyalty[1][2].
- Jack Lowden as River Cartwright, an up-and-coming MI5 agent who joins Slough House after a public blunder[1][2].
- Kristin Scott Thomas as Diana Taverner, the Deputy Director General of MI5 and head of operations[1][2].
- Saskia Reeves as Catherine Standish, the office administrator at Slough House[1][2].
- Rosalind Eleazar as Louisa Guy, an agent assigned to Slough House after a failed operation[1][2].
- Christopher Chung as Roddy Ho, a skilled computer expert and former hacktivist[1][2].
- Aimee-Ffion Edwards as Shirley Dander, who struggles with anger and drug issues[1][3].
- Kadiff Kirwan as Marcus Longridge, known for his gambling habits[1][3].
- Jonathan Pryce as David Cartwright, River’s grandfather and a retired MI5 officer[1][3].
- Hugo Weaving as Frank Harkness, a former CIA operative and River’s biological father[1][3].
These characters form the core of the show, navigating the complexities of MI5’s Slough House, a department for agents who have made career-ending mistakes.