Akugyō Chōjin (悪行超人 Evil Supermen) is a collectivist term to describe the three main branches of evil chojin: Brutal Chojin, Devil Chojin, Perfect Chojin), plus any other miscellaneous evil types. By the time of Kinnikuman Nisei, the three branches had been intentionally merged by the dMp and had become indistinct. But even previously during the Survivor Match for the Kinniku Throne Arc, the evil chojin were no longer being specified by the three branches.
Brtual Chōjin (残虐超人, Zangyaku Supermen) are Chojin who fight brutally and kill their opponents for their own amusement. They are basically Justice Chojin turned bad, and are even allowed to compete in the Chojin Olympics.
Later on, they are divided between two different unofficial factions. There are those who aid the Justice Chōjins, known as Good-Brutal Chōjin (正義の残虐超人, "Seigi" no Zangyaku Supermen). Although very brutal after entering the ring, they are essentially Justice Chōjins. Then there and those who oppose the Justice Chōjins, known as Evil-Brutal Chōjin (悪の残虐超人, "Aku" no Zangyaku Supermen). They mostly appear in the sequel series.
In the broader definition, the Akuma Chojin are a race of Chojin who reside in the Demon Realm (魔界, Makai) (or are their descendants). The race was founded by Satan (サタン), who had done so for the sole reason of obtaining the power of the General Stone (ジェネラル・ストーン).
In the more narrow definition, they are Chojin who have sold their bodies, minds, and blood to Satan and follow his will through different factions: The Seven Devil Chojin (7人の悪魔超人, Shichi-nin no Akuma Choujin), Six Devil Knights (悪魔六騎士, Akuma Roku Kishi), and Demon Seed (悪魔の種子) all fight against the Justice Chojin under the control of Satan. Additionally, the Nightmares (ナイトメアズ) was formed by a former Demon Knight, Sunshine.
(More to Come)