Koichi Yamadera (山寺 宏一 Yamadera Kōichi) is a Japanese voice actor that affiliated to Across Entertainment.
- Ultraman G - Voice dub of Lloyd Wilder
- Denkou Choujin Gridman: boys invent great hero - Voice of Takeshi Todo
- The・Ultraman: Jackal vs. Ultraman: Voices of Demon King Jackal, Zoffy, Melos and other male characters
- Ultraman Orb The Movie: Lend Me The Power of Bonds! - Voice of Alien Gapiya Sadeath
- Ninja Scroll - Voice of Jūbei Kibagami
- Cowboy Bebop - Voice of Spike Spiegel
- Dragon Ball Z: Battle of Gods - Voice of Beerus: The God of Destruction
- Ghost in the Shell - Voice of Togusa
- Mashin Eiyuuden Wataru - Voice of Kurama Wataribe
- Neon Genesis Evangelion - Voice of Ryoji Kaji
- Anpanman - Voice of Cheese
- Ranma ½ - Voice of Ryōga Hibiki
- Lupin III - Voice of Koichi Zenigata (replacing the late Goro Naya)
- One Piece - Voice of Donquixote Rosinante
- Hunter x Hunter (2011 version) - Voice of Silva Zoldyck
- Samurai Pizza Cats - Voice of Bad Bird
- Sword Art Online - Voice of Akihiko Kayaba
- Danganronpa V3: Killing Harmony - Voices of Monokuma Kubs
- Mario Kart Arcade GP 2 - Voice of Color Commentator (JP)
- Batman Ninja - Voice of Bruce Wayne/Batman
- Koichi Yamadera's favorite Ultra Warriors are Ultraman, Ultraseven and Ultraman Ace.
- Discounting the Jackal vs Ultraman, Sadeath in Orb the Movie is his first role in the Ultra Series since Lloyd Wilder in Ultraman G. Because of this, he was excited to return to the franchise and casted as Sadeath. Although initially nervous about this role, the director encouraged ad-libs in his role.
- He's also known for his versatile range, as protagonists, antagonists, and even to the point of voicing as a female.
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