Brian Cox, the acclaimed Scottish actor, has an extensive career in film, television, and theater, and has also contributed his distinctive voice to several animated projects. While much of his work has been in Western animation, he took on a prominent role in the Japanese anime feature film The Lord of the Rings: The War of the Rohirrim. This film represents his most high-profile entry into the anime medium.

In The Lord of the Rings: The War of the Rohirrim, directed by Kenji Kamiyama, Cox provides the voice of Helm Hammerhand, the mighty King of Rohan. This anime feature, set 183 years before the events of The Lord of the Rings trilogy, tells the story of Helm's final stand against an invading army, an event which leads to the fortress later being known as Helm's Deep. Cox described the character as a man of action with a fierce, almost demonic drive, but also possessing a softer side, particularly in his relationship with his daughter, Héra. He compared playing the role to his experiences performing Shakespearean kings like King Lear, drawn to the character's commanding presence and emotional depth. In promotional interviews, Cox discussed the imaginative aspect of voice acting, noting that he approached the process by tapping into childhood feelings of pretend play, and he recorded many of his lines during the COVID-19 pandemic, sometimes from his own closet. He also expressed that the role allowed him to connect with a character who is "larger than myth".

Prior to this anime role, Cox voiced the character Richard Morgan in the 2002 supernatural horror film The Ring. While not an anime, this role demonstrates his experience in genre filmmaking and voice performance. Other voice acting credits in his filmography include the character of Ward Abbott in a dubbed version of The Bourne Ultimacy, Action 12 Reporter in the animated film Fantastic Mr. Fox, Alan Watts in the film Her, and roles in animated series such as Danny Phantom, Shakespeare: The Animated Tales, Superman: The Animated Series, and the film Terra. He also narrated an audiobook of J.R.R. Tolkien's The Legend of Sigurd and Gudrún in 2009.

In The War of the Rohirrim, Cox worked alongside a cast that included Gaia Wise, Luke Pasqualino, and Miranda Otto, who reprised her role as Éowyn from the live-action films. The film was produced by New Line Cinema and Warner Bros. Animation, with Cox collaborating with director Kenji Kamiyama, known for his work on Ghost in the Shell: Stand Alone Complex and Blade Runner: Black Lotus. Following the film's release, Cox commented on the quality of voice acting in the anime industry, expressing some disappointment with what he perceived as a decline in standards during the production of the film.