Yamadera made his debut as a seiyuu in 1986 playing the role of Otter in the anime Bosco Daiboken.
After the death of veteran seiyuu Kei Tomiyama, Yamadera took on many of his ongoing roles to replace the late voice actor.
Yamadera is known to have a wide vocal range and is sometimes known as Shichishoku no Koe wo Motsu Otoko (The Man Who Has the Voice of Seven Colors). The majority of characters he plays are comedic, cool or heroic.
Yamadera teamed up with Hisako Oshima and participated in the second season of the show Shall We Dance?, the Japanese version of Dancing with the Stars, and was crowned the champion.
On the 4 episode OAV Toki-iro Kaima, Yamadera performed the 3rd ending theme "Secret City" along with Wayu Suzumiya.
Yamadera has made a guest appearance at many special events throughout Japan including the "7th Nihon Anime Festival" on March 3-4, 1990; the "Pioneer OAV Festival 94" on August 21, 1994; the "Radio Big Bang public recording" on July 25, 1999; the "Tokyo International Anime Fair (main stage)" on March 28, 2004 and the "Anime Quiz event at Tokyo Kokusai Anime Fair" on March 26, 2006.
Yamadera has dubbed several English works in Japanese. Some characters he has dubbed includes the voices of Austin Powers and Dr. Evil in the live action movie, Austin Powers: International Man of Mystery, Mammoth Manny in the animated movie Ice Age, Donkey in the animated movie Shrek 2 Bert in the classic film Mary Poppins and Éomer in the Lord of the Rings trilogy.
Other roles Yamadera has played but are not currently credited for includes his voice work as Tienshinhan in the popular anime, Dragon Ball Z, in episodes 82 and 84 only, Brent Furlong in In Sakura Wars: The Movie, Tochirou Ouyama in the OAV Queen Emeralds, Togusa in Ghost in the Shell: Stand Alone Complex and Akehiko in the OAV Tokyo Revelation.
Yamadera performed the 4th ending theme song "RANMA", along with fellow seiyuu in a group called the "Operatic Troupe", on the anime Ranma ½.
Yamadera has been the main host of the children's entertainment program Oha Star.
On August 22, 1990, Yamadera released his very first album, Glory Days. On December 16th, 1992 (almost 2 years later), he released his 2nd album, Breath.
Yamadera has co-starred and worked with fellow seiyuu, Megumi Hayashibara, in various animes. Among these are Cowboy Bebop, Neon Genesis Evangelion, and Ranma ½.
Both Yamadera and his wife, Mika Kanai, work together voicing characters on the Japanese anime cartoon show, Soreike! Anpanman.
Yamadera has voiced characters in several Japanese video games such as Johnny Shiden in Tales of Destiny, Spike Spiegel in Cowboy Bebop, Desert Claw & the Narrator in Rogue Galaxy, Susumu Kodai in Space Battleship Yamato and Duke Fleed in Super Robot Taisen Impact.
Yamadera has voiced characters in several CD dramas including his role as Migel in Fam & Ihrlie, Papachariino in Photon, Kouichi Ohtani in Sokkou Seitokai, Troubador in Aa Megami-sama Tokuten Ou and Shigemitsu Hashiba in Combination.
Yamadera released his first single on January 21, 1991 entitled "Haikei Akane-san".
Yamadera works for the Tokyo Actor's Consumer's Cooperative Society, also known as Haikyou.
Yamadera stands in at 176 cm (5 feet, 9 inches) tall, weighs approximately 67 kg (148 lbs) and has blood type A.
When Yamadera plays a radio personality, he goes under the name Bazooka Yamadera.
Yamadera made a television appearance on a show called Mini Moni's Brementown Musicians.
In the hit video game, Kingdom Hearts, Yamadera dubbed the voices of Beast in "Beauty and the Beast", Sebastian in "The Little Mermaid", Genie in "Aladdin" and popular Disney character, Donald Duck.
In his foreign dubbing work, Yamadera has dubbed the voices of famous American actors such as Tom Hanks, Brad Pitt, Eddie Murphy, Robin Williams, and many others.
Yamadera's voice fits in the category of baritone.
Yamadera played a small live action role in one of the Godzilla movies, Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack.
Yamadera has voiced a role in numerous Pokemon movies. His roles are as follows:
Mew in Pokemon - The Movie: Mewtwo Strikes Back.
Lugia in Pokémon: The Movie 2000
Deibitto in Pokémon 3: The Movie
Hunter in Pokémon 4Ever
Rossi in Pokemon Heroes - Latias & Latios
Butler in Pokémon: Jirachi Wishmaker
Professor Lund in Pokémon: Destiny Deoxys
Aaron in Pokémon: Lucario and the Mystery of Mew
Jack Walker in Pokémon Ranger and the Prince of the Sea: Manaphy
Kouichi: I listened to the recordings of Mr. Toyama all the time. I was also a big fan, so I did all sorts of research.
Kouichi: Of all the stuff Mr. Matsumoto's done, I think this is the most difficult(the original work on "Harlock Saga"). There were moments when I was left going "Huh?", but I think it's a really cool story. In the many times I've spoken with him directly, I've seen how his attitude is so forward-looking. He has so many things to tell about this world today. Dreams, hopes, romance... And the scale of the story is so huge. I don't think anyone else has told a story of this scale before.
Kouichi: In any case, enjoy the show (Harlock Saga). I hope that this story of immense scale transcends the ages, so guard it well for future generations to enjoy.