Theodore Roosevelt Jr. was the 26th president of the United States, serving from 1901 to 1909. Previously serving for six months as vice president under William McKinley, Roosevelt became president after McKinley's assassination in 1901. He was 42 years old upon his first inauguration, making him the youngest person to hold the office. Born: October 27, 1858 Died: January 6, 1919 In office: September 14, 1901 – March 4, 1909 Wiki link