Robert Firth, who provides the voice for the New York City Ring Announcer, was delighted to have had an opportunity to work with the legendary filmmaker Stephen Frears. During their ADR session, when Firth recorded the character's voice for the film's crucial Ali victory, he and Frears spent a great deal of time searching for just the right regional accent - to help capture the proper tone and manner for that period of time in American culture. Firth was taken aback by Frears' meticulous attention to detail, and Frears was intrigued by Firth's seemingly endless options he was offering to the director - so much so, that when he was leaving, a somewhat curious Frears asked the actor for his last name. He replied, "It's Firth, like Colin Firth, but without all those awards."
William Brennan at one point refers to Bryon White as 'Whizzer'. That was White's nickname from when he was a distinguished football player, leading the NFL in rushing yards with the Detroit Lions in 1940.
This is the second time Benjamin Walker has portrayed a southern lawyer on film. He portrayed lawyer Abraham Lincoln in Abraham Lincoln: Vampire Hunter (2012).