Kengo Hanazawa is a Japanese manga artist known for creating several notable seinen manga series, including Under Ninja, which received an anime television adaptation in 2023. He was born on January 5, 1974, in Hachinohe, Japan. Before becoming a professional manga creator, he worked in a printing plant for three years and later served as an assistant to the manga artist Osamu Uoto. He made his professional debut in 2004 with the series Ressentiment, which was serialized in Big Comic Spirits. This was followed by Boys on the Run, which ran from 2005 to 2008 and was later adapted into a live-action film.

Hanazawa achieved significant critical and commercial success with his next major work, I Am a Hero, which was serialized from 2009 to 2017. The series, which follows a manga artist struggling to survive a zombie apocalypse, earned him widespread recognition for its detailed artwork and unique take on the horror genre. In 2013, I Am a Hero won the 58th Shogakukan Manga Award in the general category. The series was also adapted into a live-action film directed by Shinsuke Sato.

In 2018, Hanazawa began his ongoing series Under Ninja, published in Kodansha's Weekly Young Magazine. The story is set in a modern-day Japan where ninjas secretly exist and work in various sectors of society. An anime television series adaptation of Under Ninja, produced by Tezuka Productions, aired from October to December 2023, marking the first time one of his works was adapted into an anime. A live-action film adaptation of Under Ninja was released in Japanese theaters in January 2025.

Hanazawa is known for creating protagonists who are often ordinary, introverted, or socially awkward individuals. He has stated that he identifies with these types of characters, finding it essential to establish a point of contact with them, and that he would find it less authentic to draw a perfect, invincible superhero. His art style is noted for its high level of detail and its blend of gritty realism with dynamic action sequences. He has described his work process as slow, a trait he has carried throughout his career, and he prefers to work with a small team. He is married to Julie Okamoto, a former assistant on his manga who has also published her own work.