|Born:||June 17, 1961, Shiogama, Miyagi Prefecture, Japan|
|Years active:||1985 - now|
|Spouse:||Mika Kanai (1994-2006, divorced)|
Rie Tanaka (2012-present)
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 heroes - Voice of Takeshi Todo
- The・Ultraman: Jackal vs. Ultraman: Voices of Demon King Jackal, Zoffy, Melos
- Ultraman Orb The Movie: Lend Me The Power of Bonds! - Voice of Alien Gapia Zadeath
- 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
- 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)
- Lilo and Stitch (Japanese dub) - Voice of Stitch
- Shrek (Japanese dub) - Voice of Donkey
- One Piece - Voice of Donquixote Rosinante
- Koichi Yamadera's favorite Ultra Warriors are Ultraman, Ultraseven and Ultraman Ace.
- Discounting the Jackal vs Ultraman, Zadeath 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 Zadeath. Although initially nervous about this role, the director encouraged ad-libs in his role.