Gekiga is a style of Japanese comics started in 1957. In Japan, there is a distinction between Gekiga andManga.
The style was largely pioneered byYoshihiro Tatsumi who would eventually coin the term to further differentiate it from the other comics in the day.
"Manga" means "humorous pictures"; "gekiga" was designed as a parallel word meaning "dramatic pictures", reflecting the fact that gekiga was intended for older readers (manga at the time was aimed almost exclusively at pre-teens) and was much more serious than the other Japanese comics of the day. The drawing style and the stories had a stark realism to them and often depicted the struggles of the everyday man in Japan.
Eventually the style and its growing influence amongMangaka lead toOsamu Tezuka writing in the style as well. Many of Tezuka's works near the end of his career areGekiga or influenced by it such asPhoenix andAdolf. Tezuka's embracement of the style lead to an even stronger boom in the realm of experimental comics.
Eventually the influence of gekiga began to fade as Japanese comics became more and more commercialized; mainstream comics for adult readers eventually developed intoSeinen. Currently the term refers to modern alternative manga, as well as the 60's and 70's originals.