Legendary God is a song from the NES port of Rygar. It was composed by Michiharu Hasuya. The song was later known for its use in the game Dr. Jekyll and Mr. Hyde. Though some speculate that game's developer (Advance Communication Company) lifted the tune from Rygar, both games shared the same sound designer.
Hasuya wrote the music using hexadecimal numbers for notation into his sound engine.
Dr. Jekyll and Mr. Hyde (NES)
For unknown reasons, Hasuya decided to re-use the Legendary God tune from Rygar in Dr. Jekyll and Mr. Hyde to serve as the game's title screen theme. It could have been because either Hasuya thought the song fit the overall theme of the game and/or he was under heavy time constraints and figured it would be easier just to use an earlier composition.
This version of the song is different from the version heard in Rygar; instead of the key of A, it is transposed down two steps in the key of G. Also, this version of the song does not loop.