Doctor only appears in the Elona+ version of Elona. He is the only friendly NPC that you have to interact with to finish the main quest of Elona+. He resides in Melugas, which is in the middle of the South Tyris continent. He's located in the northeast of Melugas, directly east of the well and in a small room with a Gene machine. He can be copied with an Astral Light Pen if the conditions are met.