Kentarō Kumagai is a Japanese voice actor born on February 16, 1994, in Okinawa Prefecture. He is affiliated with the talent agency Tokyo Actor's Consumer's Cooperative Society, commonly known as Haikyō.

Kumagai's path to voice acting began in his second year of middle school after he happened to see a music video by fellow voice actor Mamoru Miyano on television. He found the performer captivating, and his interest deepened when he watched the anime Mobile Suit Gundam 00, in which Miyano starred. Seeing Miyano's name at the top of the credits made Kumagai realize that voice acting was a distinct profession and inspired him to pursue it himself. Before this, he had played soccer from elementary through junior high school, an experience that informs some of his later sports-oriented roles.

After graduating from the Sogo Gakuen Human Academy in 2014, he entered the Haikyō Voice Actors Studio as part of its 45th intake. He began his professional career in 2015 under the Haikyō agency.

Kumagai's early career consisted of numerous supporting roles in television anime. His first major lead role came in 2018 when he was cast as Theo Cornaro in the fantasy series Record of Grancrest War. He portrayed Theo, a young lord navigating political intrigue and magical conflict, a performance that brought him early recognition. That same year, he also voiced the recurring role of White Blood Cell 4989 in the popular educational series Cells at Work! and Yūma Gojō in the sumo-themed sports anime Hinomaru Sumo.

He continued to gain prominence with roles in a variety of series. In 2020, he voiced Han Daewi in the action-packed The God of High School, a stoic martial artist and loyal friend, and Makoto Someya in the rugby anime number24. He also played Gaga in Drifting Dragons, Shinnosuke Kamei in The Millionaire Detective - Balance: UNLIMITED, and Makoto Majima in Ikebukuro West Gate Park. His role as Omi Fushimi in the A3! franchise, beginning in 2020, added another notable character to his filmography.

In the years that followed, Kumagai's career continued to expand across genres. His credits from this period include Hyakutarō Senju in Tribe Nine, Ryūichi Takeshima in the football anime Aoashi, Dance Dark in Lucifer and the Biscuit Hammer, and Ichiro Androalphus in Welcome to Demon School, Iruma-kun. He also voiced Shura in Hallelujah: Unmei no Sentaku, Jimmy in Yarichin Bitch-bu, and Rajak Kertia in Noblesse. A significant milestone came in 2024 when he was cast as the protagonist Laios Touden in the critically acclaimed fantasy comedy anime Delicious in Dungeon. His portrayal of the enthusiastic and quirky adventurer obsessed with monster cuisine became a defining role. In the same year, he took on the role of Chang Balroad in the second season of Tower of God, titled Tower of God: Workshop Battle.

Outside of anime, Kumagai is also active in video games and drama CDs. He is known for his role as Hideo Akuno in The Idolmaster SideM franchise, a recurring collaboration that began in 2017. He has also lent his voice to games such as Summer Pockets and Shin Megami Tensei V. In the realm of dubbing, he provided the Japanese voice for Xavier Thorpe in the live-action series Wednesday.

Kumagai holds a PADI Open Water Diver license and has maintained his interest in sports, particularly soccer and watching professional wrestling. His passion for wrestling has led to guest appearances as a commentator for DDT Pro-Wrestling events in 2021 and 2024.