Michael Shannon stars as President James A. Garfield, with Matthew Macfadyen portraying his assassin, Charles J. Guiteau. The ensemble includes Betty Gilpin as Lucretia Garfield, Nick Offerman as Chester A. Arthur, and Bradley Whitford as James Blaine, among others. Key cast members across the series:

• Michael Shannon as James Garfield
• Matthew Macfadyen as Charles Guiteau
• Betty Gilpin as Lucretia Garfield (First Lady Crete)
• Nick Offerman as Chester A. Arthur (Vice President)
• Bradley Whitford as James Blaine (Senator)
• Shea Whigham as Roscoe Conkling (Senator)
• Tuppence Middleton as Kate Chase Sprague
• Laura Marcus as Mollie Garfield
• Ben Miles as George Scoville
• Paula Malcomson as Franny Scoville
• Alistair Petrie as John Sherman
• Bronagh Waugh as Myrna
• Kyle Soller as Robert Todd Lincoln
• Željko Ivanek as Dr. Bliss
• Shaun Parkes as Dr. Charles Purvis
• Other supporting cast: Christine Grace Szarko, Barry Shabaka Henley, Nicholas Woodeson, and more

If you’d like, I can compile a precise, up-to-date cast list with character names and brief bios from current sources.