According to legend, the Four Barons of Hell were sort of like Satan's right hand men. The first one was mainly featureless with only one eye. The second one had a huge horn and gruesome teeth. The third was the color of blood and had six eyes. The fourth was black as the night and had abnormally long arms. The strangest part about the Four Barons of Hell is that there are no records of them anywhere. Contrary to poular belief, they were not written about in Dante Alligheri's Divine Comedy and they are not in Judeo-Christian Mythology.
So, where did the four barons come from? Apparently there were a hoax created by a Neon Genesis Evangelion otaku to resemble the first four Evas; claiming the creators of Evangelion based the Evas on the Four Barons of Hell. That is false, as Hideaki Anno said that the Evas were based on the Japanese oni.