Yōichi Kobiyama is a Japanese voice actor and actor born on August 15, 1959, in Tokyo, Japan. He is also known by the birth name Ryō Kajiwara, which he uses as a pen name for his writing work.

Kobiyama is best known for his voice role in the Transformers franchise. He provided the Japanese voice for the character Gigatron, also known as Devil Gigatron, in the anime series Transformers: Car Robots, which was released internationally as Transformers: Robots in Disguise. In this series, Gigatron is the leader of the Predacons and a powerful six-changing villain who eventually upgrades into Galvatron. His performance as the primary antagonist is his most recognized voice acting credit.

Beyond his work on Transformers, Kobiyama has appeared as an actor in several Japanese films. His film credits include roles in Akumu Tantei (Nightmare Detective) from 2006 and the 2016 kaiju film Shin Gojira (Shin Godzilla). These roles demonstrate his work as a live-action actor in addition to his voice over career. He has been active in the entertainment industry since at least the year 2000, when Transformers: Car Robots was released. Information about other specific voice roles or recurring creative collaborations with particular directors or production studios is not available in public records.