A versatile leading man and supporting player whose folksy, avuncular nature often disguised his true acting firepower, Hal Holbrook was best known to audiences for his portrayal of American humorist Mark Twain in his Tony Award-winning one man show “Mark Twain Tonight!” which he performed some 2,000 times between 1959 and 2005. Stage gave him his best showcases, but he was frequently praised for his television work, most notably in “Pueblo” (1973), “That Certain Summer” (1973), and the title role in “Lincoln” (1976). Film success was sporadic, though he was well cast in “All The President’s