Ryūichi Kosugi is a Japanese comedian, actor, and voice actor born on July 5, 1973, in Kyoto Prefecture, Japan. He is best known as the tsukkomi of the comedy duo Black Mayonnaise, a role he performs alongside his partner Takashi Yoshida. He is represented by the talent agency Yoshimoto Kogyo. While his primary career is in comedy and television hosting, including as a regular on the long-running variety show The Observation, Kosugi has also taken on several notable voice acting roles.

In 2011, Kosugi contributed to the anime film Fullmetal Alchemist: The Sacred Star of Milos, providing voice work for a character. He expanded his voice acting repertoire in 2015 by participating in the Japanese dub for the Marvel superhero film Ant-Man, where he voiced Luis, the fast-talking friend of the title character. He appeared at a publicity event for the film alongside actress Yuki Uchida, where he discussed his enthusiastic approach to the recording process. In 2016, he voiced the character Wandao in the television anime series Chōnōken Wandafuru.

In 2025, Kosugi took on the role of Humpty Dumpty in the anime series Fushigi no Kuni de Alice to -Dive in Wonderland-. This casting continues his pattern of performing in character roles within animated productions. His work demonstrates a career that, while rooted in live comedy and entertainment, has consistently included significant contributions to voice acting for both film and television.