Hans-Rainer Müller is a German actor and voice actor, born on 3 October 1945 in Zwickau, Germany. He is primarily known for his extensive work in the German dubbing industry, providing German voices for characters in numerous international films and television series. His career includes on-screen roles in German television productions during the 1980s, such as appearances in the series Heimat and Derrick.

Müller has built a prolific career in German voice acting, with some of his most prominent and long-running roles being the German voice of Krusty the Clown and Grandpa Simpson in the animated series The Simpsons, as well as the voice of Bender in the German dub of Futurama. His work in dubbing also extends to live-action films, with credits including the German-language versions of The Hobbit: The Battle of the Five Armies and 50/50.

In addition to these well-known roles, Müller has contributed extensively to the German dubs of anime series. His work in this area is documented across numerous productions, with his anime voice acting roles spanning from the late 1990s to 2022. A significant example of his anime dubbing work is his involvement in the Transformers franchise, where he voiced a multitude of characters in the German version of the original Generation 1 series, including Bumblebee, Cyclonus, Optimus Prime, and Ironhide, among many others. The extensive list of characters he voiced in this single series highlights his versatility and significant contribution to bringing anime to German audiences. While Müller is confirmed to have voiced Gairam in the One Piece special 3D2Y: Overcoming Ace's Death! Luffy's Pledge to His Friends as mentioned in the prompt, this specific credit could not be verified through the search results provided.