The reason for the confusion might be that there is a card called "Dark Magician of Chaos" which is a powerful fusion monster made with "Dark Magician" and "Chaos Emperor Dragon - Envoy of the End". It's a very common misconception to think the "Dark Magician of Chaos" is the "Old Dark Magician".
Dark Magician is a very well-known monster in the "Yu-Gi-Oh!" franchise and was the signature monster of Yugi Muto in the original anime.