Chester Alan Arthur was the 21st president of the United States, serving from 1881 to 1885. He was a Republican from New York who previously served as the 20th vice president under President James A. Garfield. From Wikipedia
The series adapts Candice Millard’s Destiny of the Republic with Michael Shannon as Garfield, Matthew Macfadyen as Guiteau, Mike Makowsky as creator, Matt Ross directing, David Benioff, D. B. Weiss, Bernie Caulfield as executive producers.