He voiced Nunb in the Kalenjin language, his native tongue, as well as in Kikuyu.
When Rotich provided the voice for Nien Nunb in Return of the Jedi, he was a student on work experience that happened to be on set whilst the director of the film, Richard Marquand, was looking for someone to record lines for Nien Nunb.
Rotich reprised his role 30 years later in The Force Awakens, and then again in The Rise of Skywalker. He did not play Nien in the second installment of the sequel trilogy, The Last Jedi, as his character, Nien Nunb, does not have any lines of dialogue in that film. Later in 2019, he provided the voice for the Star Wars: Galaxy's Edge ride, Rise of the Resistance.