Masaichi Nagata (永田 雅一, Nagata Masaichi; 21 January 1906 – 24 October 1985) was a Japanese businessman, film producer, horse owner [ja], and a professional baseball team owner. He served as president of Daiei Film and was the self-proclaimed creator of the kaiju Gamera, and was also the owner of the Chiba Lotte Marines-predecessor Daiei Stars, and the first president of the Pacific League.

Masaichi Nagata was a prominent businessman among variety of fields in life. His achievements to contribute in the golden era of Japanese film industries granted a title "Father of the cinema" (Japanese: 映画界の父, Hepburn: Eigakai no Chichi) in Japan, while his well-known nicknames "Nagata Trumpet" (Japanese: 永田ラッパ, Hepburn: Nagata Rappa) and "Fixer of the political world" (Japanese: 政界の黒幕, Hepburn: Seikai no Kuromaku) were given due to his boasting behaviors and connections with political circles. He had additional nicknames "Movie Demon" (Japanese: 映画の鬼, Hepburn: Eiga no Oni) and "The Last Activist" (Japanese: 最後の活動屋, Hepburn: Saigo no Katsudōya).

Either Masaichi or Hideo Matsuyama [ja], the inventor of the "Silver Week", was also the inventor of the advertising slogan "Golden Week".

He had never married in life, yet had engaged in multiple love affairs and had biological children and grandchildren. One of his alleged mistresses was the actress Machiko Kyō. He had a particularly close lover who was a student of odori dance under the actor/comedian Yukitarō Hotaru. She had introduced Yukitarō to Nagata, and Yukitarō's apprentice Yukijirō Hotaru believed she was the actual spouse of Nagata.

His biological and non-biological relatives include Hidemasa Nagata (son), a film and television producer Mamoru Nagata [ja] (grandson), Masashi Nagata (grandson) who is the current chairman of Nagata Kikaku founded by Masaichi, a businessman Masao Nagata (great-grandson) known as the YouTuber "Nagata Trumpet", Ichikawa Raizō VIII's wife Masako Ōta (adopted daughter), and his nephew-in-law Masayuki Tayayama [ja] is the first professional taiko player in Japan.

Masaichi was born into a ton'ya for yūzen and dye in Kyoto, however his family underwent misfortunes since when Masaichi was three-years-old, and eventually fell apart; loss of the factory by a fire, an elopement by a kozō [ja] (employee) and a jochū (housemaid) who stole money when they escaped, and the bankruptcy due to his father being a joint guarantor of his friend. Masaichi attempted to became a kozō for one of his relatives (an executive director of Tokyo Stock Exchange) to reconstruct the family for his parents. To gain a sufficient educational attainment, he attended the Ōkura College of Commerce [ja] (now Tokyo Keizai University), however lost his father due to an intracranial hemorrhage and dropped out the school in despair. As a member of a local seinendan, he diligently contributed in the cleaning of damaged cites following the Great Kantō Earthquake, and subsequently returned to Kyoto.

Nagata was gradually influenced by socialism due to his admire for heroism, and joined a local yakuza Senbongumi afterwards. He, along with Jun Okamoto [ja], became one of apprentices of Suezaburō Sasai [ja], while Nagata defended Suezaburō and his father and the crime boss Sanzaemon; Sanzaemon was a renowned kyōkaku known as ""Fierce Tiger" (Japanese: 荒虎, Hepburn: Aratora)", and Nagata claimed Sanzaemon definitely not being an actual yakuza, and Suezaburō was the 10th highest taxpayer in Kyoto back then. However, Masaichi's mother strongly deplored the fact that her son became a subject of surveillance by the police, and she expelled Masaichi from the family.

He joined the Nikkatsu studio in 1925 due to his relationships with the aforementioned Shōzō Makino and the Makino Family [ja], and after working as a location manager, rose to become head of production at the Daiei Kyoto studio [ja]. As a fledgling handyman, Nagata was noticed for his eloquence and social skills, and was favored by notable figures (such as Yoshirō Fujimura, Nobuo Asaoka [ja], Mochizuki Keisuke, and so on), and developed a relationship with the political world. Experiencing conflicts with the Nikkatsu president, he left the company in 1934, taking many Nikkatsu stars with him, to form Daiichi Eiga. While short-lived, that studio created such masterpieces as Kenji Mizoguchi's Sisters of the Gion (1936) and Osaka Elegy (1936).