Masashi Hironaka is a Japanese voice actor and narrator born on December 27, 1957, in Tokyo's Shibuya district. He is affiliated with the talent management firm Aoni Production. His path to a career in voice acting began at a young age; he joined a children's theater group at the age of ten following a recommendation from his school, an experience that shaped his early performance skills. He later studied film at Nihon University College of Art. After graduating, Hironaka initially worked in stage performance and as a product demonstrator before fully committing to voice acting, a decision influenced by his future wife. His entry into the industry was facilitated by a demo tape he submitted to Aoni Production, leading to his professional debut.

Hironaka is most closely associated with the role of Siegfried Kircheis in the legendary OVA series Legend of the Galactic Heroes. He voiced the character across multiple installments, including the main series, the films My Conquest is the Sea of Stars and New Wars' Overture, and the gaiden series A Hundred Billion Stars, A Hundred Billion Lights and Spiral Labyrinth. He holds this role in very high regard, considering it his career-defining work and has expressed a deep willingness to reprise it. His association with the series also connected him with fellow lead voice actor Ryō Horikawa, who noted in an interview that he and Hironaka were the youngest members of the main cast.

Beyond his signature role, Hironaka has built a extensive career spanning anime, narration, and commercial work. He has taken on a wide variety of anime roles, demonstrating his range. Examples of his work include Ihika in Fairy King, Doryū as well as Wingwaver and the combined form Landcross in Transformers: Victory, Hiromi Ikeda in Karura Mau and its film adaptation, Shūichi "Bird" Torigai in Blue Sonnet, Kimihiko Masumi in Kishin Corps, Zackt in Record of Lodoss War, and Christof in Monster. While he continued to take anime roles, such as providing narration for Pop Team Epic, a significant portion of his career has been dedicated to narration. He is a prominent narrator for Japanese television, lending his voice to numerous programs for major networks like Nippon TV, TBS, and TV Tokyo, including shows such as Sekai Marumie! and Sunday Japan. His voice is also a familiar presence in commercials, radio dramas, and video games.