Takeharu Ōnishi, also known as Takeharu Oonishi or Takeharu Ohnishi, is a Japanese voice actor and stage actor. He was born on July 8, 1967, in Nara Prefecture, Japan. He is affiliated with the talent agency Arts Vision and is a founding member of the theater company Akapera. Ōnishi speaks the Kansai dialect and is married to fellow voice actress Masayo Kurata.

Ōnishi has built a career spanning over two decades, accumulating a substantial number of credits across both television anime and film. He voiced Madarao in the 2006 series Kekkaishi, a role he performed for all 52 episodes. In the same year, he began voicing Ametarou in Pururun! Shizuku-chan and its sequel Pururun! Shizuku-chan Aha, as well as the character Hanatare-kun in the same franchise. He also provided the voice of Yamamoto in the long-running series Atashinchi, appearing in over 660 episodes.

In the 2000s, his roles included Toshiaki Hayami in Guyver: The Bioboosted Armor, Kawai Tsuginosuke in Intrigue in the Bakumatsu – Irohanihoheto, and a guest role as Gukku in Death Note. During the 2010s, he appeared in Hunter x Hunter as Worm, Tocino, and Cherry, and voiced a delinquent and an ancient languages teacher in Parasyte -the maxim-. His film work from this period includes the role of Murata Tetsuya in Gintama: The Movie, a producer in Case Closed: The Crimson Love Letter, and an Anaheim Electronics plant manager in Mobile Suit Gundam: The Origin IV – Eve of Destiny.

More recently, Ōnishi has taken on significant roles in major productions. He voiced Kenjirō Takōda in the 2024 series The Fable. He also voices Gerozaemon Geroda in the 2025 series Yaiba: Samurai Legend. These recent credits demonstrate his continued active presence in the industry. Throughout his career, he has also lent his voice to characters in series such as Fortune Quest L, Space Symphony Maetel ~Ginga Tetsudō 999 Gaiden~, Dinozaurs: The Series, Sugar Bunnies, Tamagotchi! Miracle Friends, Monkey Turn, Monkey Turn V, Transformers: Dark of the Moon, and Ai no Wakakusayama Monogatari.