This was a series of books, thy would have been around in mid 1985, and the artwork on the covers was much like Terry Patchett's book art...
The male character was transported from the "modern" world to an alternate world. He was a biker and a hell raiser, but in the alternate world he finds he's a magician/wizard. He is mentored by a wizard. I hope I'm not mixing up books, but I think there was a female character who was transported also, and she becomes in the "alt world" a warrior.
If I'm not mixing my story lines, there was also an "evil" called "The Dark" which hunted people and took their minds but left their bodies alive but senseless?
Seems like at least a couple of the books used the word "rune or runes" in the title. At least one of the book covers had the male character standing in front of a door with runes on it with his hand or hands up. Again, I think the title had "runes" in a couple of them.