Keiichi Sigsuga, born in 1972 in Kanagawa Prefecture, Japan, is a Japanese light novel author known for creating several long-running and influential series. His pen name is derived from SIG Sauer, a firearms manufacturer, and the given name Keiichi from the character Keiichi Morisato in the manga Oh My Goddess!. He is a self-described gun maniac and motorcycle enthusiast who cites Galaxy Express 999 and the works of Hayao Miyazaki as primary influences on his writing.

Sigsawa made his literary debut in March 2000 when his work Kino's Journey was serialized in Dengeki hp magazine after being a finalist for the 6th Dengeki Novel Prize. This series, illustrated by Kouhaku Kuroboshi, became his breakthrough and remains his most enduring work. Kino's Journey follows a young traveler named Kino and a talking motorcycle named Hermes as they visit various countries for exactly three days each, observing diverse customs, political systems, and philosophical dilemmas. The series has been published continuously since its debut and has spawned multiple adaptations. The first anime adaptation aired as a thirteen-episode television series in April 2003, produced by A.C.G.T and directed by Ryūtarō Nakamura. A film titled Kino's Travels: Life Goes On, serving as a prequel showing Kino's training, premiered on February 19, 2005. A second anime adaptation, Kino's Journey the Beautiful World the Animated Series, aired in October 2017 produced by Lerche and directed by Tomohisa Taguchi. The series also includes an OVA and a second film titled Kino's Journey: Country of Illness For You from 2007.

Beyond Kino's Journey, Sigsawa created the Tale of a Single Continent series, which includes the light novel series Allison, Lillia and Treize, and Meg and Seron. The Allison novels were published between March 2002 and May 2004, with illustrations again provided by Kouhaku Kuroboshi. A manga adaptation of Allison was serialized between July 2007 and December 2008. An anime adaptation titled Allison & Lillia, covering both the Allison and Lillia and Treize storylines, aired between April and October 2008.

Sigsawa is also known for his work within the Sword Art Online universe. He authored Sword Art Online Alternative: Gun Gale Online, a spin-off light novel series that began publication in December 2014 under the Dengeki Bunko label, again illustrated by Kouhaku Kuroboshi. The series follows Karen Kohiruimaki, a tall university student who finds confidence as her small, pink-clad avatar Llenn in the Gun Gale Online game. An anime adaptation produced by Studio 3Hz premiered in April 2018, directed by Masayuki Sakoi with series composition by Yōsuke Kuroda. A second season, Sword Art Online Alternative: Gun Gale Online II, has been announced. Sigsawa also served as the gun consultant for the Phantom Bullet arc of Sword Art Online II, reflecting his deep expertise in firearms.

Throughout his career, Sigsawa has maintained a distinctive artistic identity centered on travel, philosophical observation, and technical detail about firearms and vehicles. His works frequently feature protagonists journeying through varied landscapes and encountering societies that serve as allegorical reflections on human nature, technology, and morality. The recurring phrase from Kino's Journey that the world is not beautiful, and therefore it is beautiful, encapsulates his thematic approach of finding meaning and beauty in imperfection and complexity. His collaborations with illustrator Kouhaku Kuroboshi have produced consistent visual identities across multiple series including Kino's Journey, Allison, and Sword Art Online Alternative Gun Gale Online.

Sigsawa has expressed that he was brought up watching anime and considers the anime adaptations of his works as creations of their respective directors rather than direct extensions of his own vision. This perspective has allowed various production teams to interpret his source material while maintaining its core themes. His influence extends beyond his own creations into the broader light novel and anime industry, particularly in works involving military and firearms elements, where his expertise is frequently sought.