The Adventures of Maddog Williams in the Dungeons of Duridian is a graphic adventure released by Game Crafters in 1991 for MS-DOS, Amiga, and Atari ST.
In this fantasy title, developed by Iliad, you are Maddog Williams, and you have to save princess Leoria and the kingdom of Duridian.
Unfortunately, seeing the game's graphics, it seems it was released in 1986, not in 1991. It really looks like the very first Sierra adventures. But if you can ignore the outdated visuals, Maddog Williams is an excellent adventure, with a good plot and puzzles that you will enjoy.
This game is now freeware.
Download for PC 
Download for Mac