The New York Times reported Holbrook died at his home in Beverly Hills on Jan. 23.
Holbrook played the writer in the one-man show "Mark Twain Tonight!" He won a Tony for Best Actor in a Play in 1966 for that portrayal.
He started performing "Mark Twain Tonight!" in 1954 and continued performing the show into the 2000s at venues all over the country. He was nominated for an Emmy in 1967 for the TV adaptation of the play.
He won a total of five Emmys throughout his career. At 82, Holbrook was nominated for an Oscar for his supporting actor role in the 2007 film "Into the Wild."
Among his more notable roles was portraying the unidentified government source Deep Throat in the Watergate film "All the President's Men."
He often was cast in the roles of respected authority figures and mentors, like finance veteran Lou Mannheim in "Wall Street," and roles that included judges, doctors and senators, even President Abraham Lincoln in a 1974 miniseries.
His television credits included a regular role on "Evening Shade," both parts of the miniseries "North and South" and guest starring with his wife Dixie Carter on "Designing Women." He also appeared on "Sons of Anarchy."
I saw Hal Holbrook as Mark Twain twice, fifty years apart. He did a ton of work over the years, never less than first-rate, but the Twain performances approached perfection, and they will stay with me forever. RIP.— Michael McKean (@MJMcKean) February 2, 2021
Hal Holbrook was an American treasure. He was equally brilliant in the spotlight onstage, or in the shadows of a garage in "All the President's Men." https://t.co/E4dQ6uJCcs— Richard Roeper (@RichardERoeper) February 2, 2021