Peerless Reincarnated Demon Lord in Hero Academy is a Manga/Manhwa/Manhua in english language, ACTION series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

The demon lord is reincarnated 1000 years after his death as a young man. To find rivals for his power he enrolls in a magic academy.