Root will play FBI chief J.Edgar Hoover and Richardson will play civil rights activist Bob Moses. Root has two Broadway credits, the 1987 revival of All My Sons, and the 1986 play So Long on Lonely Street.

As previously announced, Anthony Mackie will play Dr. Martin Luther King in in the TV drama. The 2014 film "Selma" was criticized by some for presenting an distorted picture of the relationship between King and President Lyndon Johnson during the battle to pass the 1964 Civil Rights Act. The stage drama presented a much more complex picture of the same events, which formed a centerpiece of both men's careers.

Mackie is known for his performance as Falcon in the "Captain America" films and is poised to star in another historical film, a biography of runner Jesse Owens. He has appeared on Broadway three times, in A Behanding in Spokane (2010), Drowning Crow (2004) and Ma Rainey's Black Bottom (2003).

The website also reported that actress Melissa Leo has been cast in the role of Ladybird Johnson, the First Lady.

Production on "All the Way" is scheduled to commence in September. No HBO airdate has been reported. Robert Schenkkan’s drama about President Johnson’s first year in office will be directed for TV by Jay Roach. HBO acquired the rights to adapt the play in July 2014, about a month after it also won the Tony Award as Best Play. Stephen Spielberg will serve as executive producer.

Roach produced and directed Cranston in Trumbo, a film about blacklisted screenwriter Dalton Trumbo, which is scheduled for release later this year. Roach directed another politically themed 2012 HBO project, "Game Change," about Republican John McCain and Sarah Palin’s 2008 campaign for the White House.