Ryōkan Koyanagi is a Japanese voice actor and narrator from Chiba Prefecture. He is affiliated with the Tokyo Actor's Consumer's Cooperative Society, commonly known as Haikyō. His birth date is April 3rd. He graduated from the Visual Techno Academy in 2009 and began his professional voice acting career in 2010. His voice is classified as a low baritone.

Koyanagi has built a career characterized by a deep, commanding vocal presence, often cast in supporting roles that require a sense of power, authority, or physical strength. Early in his career, he appeared in numerous television anime series, including small roles in Softenni, Jormungand, BTOOOM!, Medaka Box Abnormal, and No Game No Life. One of his first recurring characters was Jumbo in the Black Butler: Book of Circus arc.

He has secured several significant recurring roles in major anime franchises. He is best known for voicing Ottar, the captain of the Freya Familia, in the series Is It Wrong to Try to Pick Up Girls in a Dungeon? He has reprised this role across multiple seasons of the main anime, its spin-off Sword Oratoria, and the theatrical film Arrow of the Orion. In the series Saga of Tanya the Evil, he voices Severin Vianto, a key member of the 203rd Aerial Mage Battalion under the protagonist's command. He also portrayed Takeshi Kido, the pangolin-type beastman, in the action series Killing Bites.

His other notable anime roles include Bold in Sword Art Online Alternative: Gun Gale Online, an orc general in That Time I Got Reincarnated as a Slime, and Morten Fredholm in Knights & Magic. He also appeared in the series The Unlimited Hyōbu Kyōsuke, Active Raid, and provided voices for the long-running anime Doraemon and Case Closed. Beyond anime, his work extends to video games, where he has contributed to titles such as White Cat Project, the Super Robot Wars series, the Nobunaga's Ambition series, and Final Fantasy XVI.

Koyanagi is also active in the field of dubbing for foreign films and television series. He has provided Japanese voices for productions such as Iron Man 3, Star Trek Into Darkness, Oblivion, Arrow, Criminal Minds, and Power Rangers Super Samurai. His voiceover work includes regular narration for television programs, notably the long-running soccer highlights show Super Soccer on TBS, and as the regular narrator for TV Champion Extreme. His hobbies include playing soccer and badminton, and he holds a standard Japanese driver's license.